Feldspars Michael J. Potter INTRODUCTION The first commercial production of feldspar in the United States occurred in about 1825 and was mined from pegmatite bodies located in Connecticut. The feldspar was hand sorted and shipped to England. During the nineteenth and twentieth centuries, feldspar production grew with new production locations, integrated mine and processing facilities, and the development in 1939 of the flotation process for feldspar by the U.S. Bureau of Mines (USBM) and the feldspar industry. The first commercial feldspar flotation plant began operations in Kona, North Carolina, in 1946 (Feitler 1967; Rogers, Neal, and Teague 1983). In 2003, U.S. production of feldspar, based on reported and estimated data, was about 800,000 t. World production of feldspar, excluding China, was an estimated 10.8 Mt (Potter 2005). Since 1980, the U.S. feldspar industry has seen some expansion of plant capacity, a few plant closures, and changes in ownership of existing operations. In its glass end-use market, the industry has been affected by glass recycling and by competition from metal, paper, and plastic containers. In ceramics, the other major market for feldspar, much of the manufacturing of plumbing fixtures and tile is in Brazil, China and other Asian countries, and Western Europe (Roskill Information Services Ltd. 2002). Brazil, China, Colombia, Italy, Mexico, and Spain are significant exporters of plumbing fixtures and tile to the United States (Ceramic Industry 2004; Grahl 2004). Feldspars make up the most abundant mineral group in the earth’s crust. They account for an estimated 60% of the exposed rocks, as well as soils, clays, and other unconsolidated sediments, and are principal components in rock classification schemes. Feldspars are aluminum silicate minerals that contain varying proportions of calcium, potassium, and/or sodium. The principal feldspar species are albite (sodium feldspar), anorthite (calcium feldspar), and microcline and orthoclase (potassium feldspars). These species are almost never found in pure form in nature but occur as mixtures of varying proportions. Pegmatites, which are one source of feldspar, are exceptionally coarse-grained igneous rocks and have a composition similar to that of granite. The composition may be simple or complex and may include minerals rich in such elements as lithium, rare earths, tantalum, and others (Jackson 1997). Perthite is a variety of alkali (sodium-potassium) feldspar in which the potassium-rich phase (typically microcline) appears to be the host from which the sodium-rich phase (typically albite) exsolves (i.e., unmixes). The exsolved areas are visible to the naked eye and typically form irregular veinlets, strings, and so forth (Jackson 1997). Antiperthites have sodium-rich plagioclase as the host feldspar and intergrowths of potassium-rich feldspar. What is commonly known as Spruce Pine alaskite is an important feldspar ore-bearing rock that occurs in the Spruce Pine District of North Carolina. This alaskite has been described as a coarse-grained pegmatitic granite (Kauffman and Van Dyk 1994). According to A. Glover (personal communication), a true alaskite has a higher potassium than sodium content, whereas the Spruce Pine alaskite has a higher sodium than potassium content. Alaskite generally contains microcline, orthoclase, and quartz; plagioclase may or may not be present (Rogers, Neal, and Teague 1983). Aplite that was mined in 2003 (in only one U.S. location, in Virginia) is a metanorthosite (metamorphosed anorthosite) with a high proportion of plagioclase feldspar. Feldspars are widely used in the glass and ceramic industry. Nepheline syenite, which is covered in a separate chapter in this book, is a light-colored, silica-deficient feldspathic rock made up mostly of sodium and potassium feldspars and nepheline. Although not mined in the United States for glass and ceramic use, nepheline syenite has been imported from Canada for a number of years for that use. A single operation in Arkansas has been producing nepheline syenite for its internal use in manufacturing roofing granules and related products. PRODUCTION AND TRADE North America U.S. production of feldspar comprises hand-cobbed, flotation concentrates, feldspar-quartz mixtures (feldspathic sand), and aplite. Beginning in 1992, aplite has been included with feldspar production data. Table 1 shows U.S. feldspar production from 1980 to 2003. Flotation concentrates comprised about 70% to 80% of output through 1991 and about 40% to 45% thereafter. Feldspar-silica mixtures and hand-cobbed material made up about 20% to 30% through 1991, and thereafter, with aplite being included, about 55% to 60% of the output. Feldspar was mined in seven states in 2003, which were, in descending order of output, North Carolina, Virginia, California, Georgia, Oklahoma, Idaho, and South Dakota. North Carolina accounted for about 45% of the total. Ten companies mined feldspar, nine of which operated 12 beneficiation facilities—four in North Carolina, three in California, and one in each of the five remaining states mentioned (Table 2). U.S. production data for feldspar are collected by the U.S. Geological Survey (USGS) by means 451 452 Table 1. Industrial Minerals and Rocks Feldspar production in the United States, kt Year Flotation Concentrate Percentage Other* Percentage Total 1980 513 80 131 20 644 1985 442 70 193 30 635 1990† 440 70 190 30 630 1995† 400 45 480 55 880 2000† 330 42 460 58 790 2003† 330 41 470 59 800 Source: USBM 1981–1996; USGS 1997–2005. * Includes hand-cobbed feldspar, feldspar-quartz mixtures (feldspar content), and (beginning in 1992) aplite. † Data rounded to no more than two significant figures because of partially estimated data. of a voluntary survey. Of the 12 known beneficiation facilities in 2003, 6 responded with production data by the survey deadline. These 6 facilities represented about 64% of the production shown in Table 1. In 1985, the response rate, by tonnage, was 81%; in 1990, 75%; and in 2000, 60%. As a result, U.S. production data in Table 1 for 1990 and after have been rounded to no more than two significant figures because of partially estimated data. Canada has had no feldspar production for a number of years, although some projects are being developed. Avalon Ventures Ltd. of Toronto, Ontario, continues work on its Warren Township, Ontario, anorthosite (calcium plagioclase feldspar) project. Also under development is the company’s Separation Rapids project near Kenora, Ontario, which has a deposit containing high-lithium feldspar, for potential use in glass and ceramic manufacture (Avalon Ventures Ltd. 2004). Another company, i-minerals inc. of Vancouver, British Columbia, continues to test and develop two feldspar deposits at its Helmer-Bovill property in Latah County, Idaho. Its Kelly’s Basin deposit contains sodium feldspar, and the “WBL” tailings (previously owned by Washington Brick and Lime Co.) contain potassium feldspar and quartz (i-minerals inc. 2004). U.S. imports of feldspar increased from 864 t in 1985 to a high of 17,900 t in 1991. Between 1999 and 2003, imports fluctuated between about 5,500 tpy and 8,000 tpy. Most of the imported material from 1986 to 2002 came from Mexico. Beginning in 2003, Turkey became a significant exporter of feldspar to the United States (Table 3). U.S. feldspar trade and apparent consumption statistics are shown in Table 4. Production of feldspar in Mexico increased from 163,000 t in 1990 to an estimated 330,000 t in 2003. Mexican exports between 1997 and 2003 fluctuated between about 5,900 tpy and 11,400 tpy, with 98% to 99% going to the United States. Mexican imports of feldspar between 1997 and 2003 were between 1,200 tpy and 5,150 tpy. The United States supplied between 86% and 98% of the total (U.N. Statistics Division 2004). Rest of World Feldspar is produced in more than 50 countries. According to preliminary data and estimates by the USGS for 2003, the following countries produced these estimated amounts of feldspathic materials: • Italy—2.5 Mt • Turkey—1.8 Mt • France—650,000 t • Germany—450,000 t • Spain—450,000 t • Czech Republic—350,000 t • Egypt—350,000 t Significant production also has come from China and countries in Southeast Asia. Table 5 shows exports from selected countries. In Italy, output in 2002 included aplite, feldspathic sand, sodium feldspar, sodium–magnesium feldspar, and sodium–potassium feldspar. Gruppo Minerali SpA and Maffei SpA are among the largest producers. Aplite mined by Maffei contains sodium feldspar (20%), potassium feldspar (40%), quartz (30%), and other minerals (10%). End uses for feldspathic products include floor and wall tile, glass, sanitary ware, and tableware. A major development in recent years has been gres porcellanato (i.e., glazed and unglazed porcelain tiles), which contain a high percentage of feldspar. Most Italian feldspar production is consumed domestically, and large quantities of the mineral are imported for the ceramics industry. Italian imports of feldspar increased from 246,000 t in 1992 to 1,865,000 t in 2001 and about 2,290,000 t in 2003 (U.N. Statistics Division 2004; 2003 data given in Table 6). Most of the imported material came from Turkey (Roskill Information Services Ltd. 2002; Crossley 2003; U.N. Statistics Division 2004). In Turkey, the majority of feldspar produced in 2003 was albite, although potassium feldspar had a small output. There were six main and six smaller producers. Two of the large companies, Çine Akmaden Madencilik Tic. A.Ş. and Esan Eczacibaşi Endüstriyel Hammadeler San. ve Tic. A.Ş., produced flotation feldspar. A third company, Kaltun Madencilik San ve Tic. A.Ş. had plans for a new flotation plant in the works in 2003. Flotation feldspar, with its increased whiteness, was being consumed by porcelain tile producers in Italy and other countries (Crossley 2003). Turkish exports of feldspar grew from 163,000 t in 1991 to 2.1 Mt in 2000. The main reason for the rapid increase in shipments was a sharp rise in demand from ceramics companies in Italy and Spain (Roskill Information Services Ltd. 2002). Turkish exports were reported to be around 2.2 Mt in both 2001 and 2002 and about 3 Mt in 2003. About 90% of the exports in 2003 went to Italy and Spain (Crossley 2003; U.N. Statistics Division 2004). In Asia, sodium feldspar is probably the most widely used feldspar because of its relative abundance, especially in China and Thailand, both of which are major exporters (Lines 2003). Although official data are not available, Chinese production of feldspar may exceed 2 Mtpy (Roskill Information Services 2002). Estimated production in 2003 for Thailand was 780,000 t and for the Republic of Korea, 400,000 t. Japan produced an estimated 50,000 t of feldspar in 2003 and an estimated 300,000 t or more of aplite (Potter 2005). Table 7 shows feldspar production for a number of selected countries. Chinese exports of feldspar in 2001 were 557,000 t, with at least 400,000 t probably being exported to Taiwan, some of which was shipped via Hong Kong. In 2003, Chinese exports were about 600,000 t, with major destinations of Indonesia, Japan, Malaysia, the Republic of Korea, Taiwan, and Vietnam. In 2001, exports of feldspar from Thailand were reported to be about 330,000 t, with about 200,000 t going to Malaysia. In 2003, Thai exports were again about 330,000 t, with major destinations of Malaysia, United Arab Emirates, and Vietnam (Roskill Information Services Ltd. 2002; U.N. Statistics Division 2004). Potentially economic deposits of feldspar occur in at least 70 countries, and the potential supply throughout the world is presumed to be large. Feldspar reserve and resource data have only been assessed for a few countries: Reserves in Brazil have been estimated at 23 Mt; in Italy, 14 Mt; and in the Republic of Korea, 36 Mt. Detailed estimates of world reserves and resources for most countries are not available or have not been compiled (Roskill Information Services Ltd. 2002). Table 2. U.S. feldspar operations Typical Analysis, % Company Ore Body Mining Milling Process Products By-products and Coproducts Size,* µm Al2O3 Fe2O3 CaO K2 O Na2O 600 21.7 0.180 5.60 02.90 5.50 None Aplite U.S. Silica Co., Montpelier, Virginia (Hanover County) Pegmatite Open pit Processing Aplite Arkhola Sand and Gravel, division of APAC, Arkansas, Inc., Muskogee, Oklahoma (Muskogee County) River sands Dredging Washing, magnetic separation, leaching Glass sand 600 05.40 0.100 0.08 03.04 0.78 Industrial sand, construction sand Granite Rock Co., Quail Hollow Quarry, Felton, California (Santa Cruz County) Marine sands Open pit Processing Glass sand 425 09.50 0.230 0.80 04.07 1.85 Clay, other sand products Oglebay Norton Specialty Minerals, Kings Mountain, North Carolina (Cleveland County) Pegmatite Open pit Flotation Glass sand na† na na na na na P.W. Gillibrand Co., Simi Valley, California (Ventura County) Deltaic conglomerates, sandstone, siltstone Open pit Washing plant with flotation Amber grade 600 09.00 0.350 1.00 04.00 3.50 Regular 600 05.00 0.150 0.50 02.00 1.25 Flint grade–high grade 600 04.00 0.040 0.30 01.50 1.00 Unimin Corp., Bryon, California (Contra Costa County) Sandstone Open pit Washing, flotation Glassil glass sand‡ 425 04.10 0.120 0.06 02.85 0.37 Industrial sand, construction sand Unimin Corp., Emmett, Idaho (Gem County) Lake deposits Open pit Washing Glassil glass sand‡ 425 08.31 0.130 0.77 02.99 2.06 Industrial sand K-T Feldspar Corp., Spruce Pine, North Carolina (Mitchell County) Alaskite Open pit Flotation Mica, industrial sand Feldspar-Quartz Mixtures Feldspathic sand is a by-product of mica and kaolin clay production. Construction sand, industrial sand Minspar 1 600 18.5 0.050 1.50 04.10 6.50 Minspar 200 075 18.5 0.060 1.50 04.10 6.50 Minsilspar§ 090 14.0 0.060 1.10 02.80 4.90 ** na na na na na NC-4 075 18.8 0.070 1.40 04.10 6.82 F-20 600 18.8 0.065 1.40 04.10 6.82 Silo-o-spar‡ 090 13.5 0.057 1.05 02.86 4.86 ** 18.6 0.070 1.85 03.80 7.20 F-1 600 19.3 0.080 1.50 04.50 6.70 F-4 090 19.3 0.080 1.50 04.50 6.70 F-4 Minspar§ The Feldspar Corp., Spruce Pine, North Carolina (Mitchell County) Alaskite Open pit Flotation Felex Unimin Corp., Spruce Pine, North Carolina (Mitchell County) Alaskite Open pit Flotation 075 19.6 0.040 1.70 06.90 4.80 Unispar 40 ** na na na na na Unispar 50 ** na na na na na Feldspars Sodium–Potassium Feldspar Mica, industrial sand Mica, high-purity quartz Potassium Feldspar Pacer Corp., Custer, South Dakota (Custer County) The Feldspar Corp., Monticello, Georgia (Greene and Jasper counties) Pegmatite Granite Open pit Dry grinding Flotation Custer potash feldspar 075 17.0 0.150 0.30 10.00 3.00 Custer potash feldspar 045 17.0 0.150 0.30 10.00 3.00 Custer potash feldspar 038 17.0 0.150 0.30 10.00 3.00 Crystalline feldspar 045 15.0 0.150 0.30 07.00 3.00 G-40 425 18.0 0.076 0.80 10.20 2.85 G-200 075 18.5 0.082 0.81 10.75 2.85 Mica Industrial sand 453 * Nominal top size. † na = not available. ‡ Mean values, do not represent a specification. § Feldspar-silica mixture. ** Submicron grind feldspar extender and filler product. Open pit, selective mining by contractors 454 Industrial Minerals and Rocks Table 3. U.S. imports* of feldspar, by country, t Table 5. Exports of feldspar, by selected countries,* kt Country 1997 2000 2003 Country 1997 Mexico 8,200 7,100 6,100 China 591 607 Turkey 0 0 1,800 † France 122 296 286 Other 400 100 100 83 61 102 8,600 7,200 8,000 Italy 43 122 165 Malaysia 21 24 53 Norway 68 71 68 Total Germany Source: International Trade Administration 2004; U.N. Statistics Division 2004. * Data rounded to two significant figures. † U.N. statistics show exports to the United States as 16,600 t. Table 4. Spain U.S. feldspar statistics, kt 2000 2003 599 25 57 66 Thailand 241 294 330 Turkey 950 2,114 3,000 Adapted from U.N. Statistics Division 2004. Year Production Imports Exports Apparent Consumption* 1980 644 0.4 11.8 633 1985 635 0.9 8.4 628 1990 630† 11.3 24.8 620† 1995‡ 880† 9.0 14.7 870† 2000 790† 7.2 11.4 790† 2003 800† 8.0 9.0 800† * Includes countries with feldspar exports of 50,000 tpy or higher in 2003. Table 6. Imports of feldspar, by selected countries,* kt Country Source: USBM 1981–1996; USGS 1997–2005. * Calculated as production plus imports minus exports. † Data rounded to no more than two significant figures because of estimated data. ‡ Beginning in 1992, aplite data are included. 1997 2000 2003 Germany 42 52 51 Indonesia 81 105 186 Italy 714 1,573 2,292 Malaysia 267 281 262 Poland 36 82 155 Portugal 36 60 81 229 552 777 Spain Adapted from U.N. Statistics Division 2004. * Includes countries with feldspar imports of 50,000 tpy or higher in 2003. Table 7. Feldspar world production, by selected countries,* kt Country 2003† 1980 1985 1990 1995 2000 Brazil 123 110 105 199 118 China‡ na§ na na na na na Colombia 27 34 35 58 55 100 Czech Republic na na na na 337 350 4 19 10 75 330† 350 France 210 172 420† 632 642† 650 Germany 381 322 418† 330 450† 450 59 46 54 100 110† 150 Iran 3 32 32 80† 156 190 Italy 345 1,116 1,610 2,199 2,500 2,500 Egypt India Korea, Republic of 75 72 145 237 368 330 400 Mexico 117 100 163 122 334 330 Poland 40† 60 32 46 165 240 41 29 44 107 120 120 103 136 214 379 460† 450 Portugal Spain Thailand 24 104 311 670 626 780 Turkey 73† 20† 182 760 1,148 1,800 United States 644 635 630 880 790 800 6 43 91 227 130 150 Venezuela Other Total (rounded) 928 977 1,412 668 699 915 3,200 4,100 6,000 7,900 9,500 10,800 Source: USBM 1981–1996; USGS 1997–2005. * Includes countries with estimated feldspar production in 2003 of 100,000 t or higher. † Estimated. ‡ Official data are not available. In 2000, estimated production may be 2 Mt or more (Roskill Information Services Ltd. 2002). § na = not available. Feldspars GEOLOGY The common feldspar minerals can be represented in a ternary phase system that shows feldspar mineralogy; the end members are KAlSi3O8 (orthoclase), NaAlSi3O8 (albite), and CaAl2Si2O8 (anorthite). The end-member compositions also are referred to as potassium, sodium, and calcium feldspar (Table 8). The feldspars whose chemistry ranges between the potassium and sodium end members are known as alkali feldspars, whereas those between the alkali and calcium end members are plagioclase feldspars. The plagioclase series is arbitrarily subdivided and named according to increasing mole fraction of the anorthite component: albite, oligoclase, andesine, labradorite, bytownite, and anorthite (Jackson 1997). The feldspar groups can be further subdivided based on structural and compositional features within the alkali or plagioclase feldspar series (Kauffman and Van Dyk 1994). The feldspars have become the primary tool in the classification of igneous rocks (Deer, Howie, and Zussman 2001). Table 8 gives theoretical end-member compositions of the principal feldspars. Minerals of the feldspar series have some similar physical properties: a Mohs hardness of 6, a specific gravity range of 2.54 to 2.76, and a vitreous luster. Color can range from colorless, white to gray, green, yellow, and red; feldspars may be translucent to transparent. Geologic Occurrence and Major Deposits The major U.S. commercial feldspar deposits in 2003 were Spruce Pine alaskite; the aplite in Hanover County, Virginia; pegmatites; and various sand deposits, including certain beach, dune, and river sands, derived from granitic source rocks. Alaskite Spruce Pine alaskite is a granitic rock that is composed principally of plagioclase, quartz, orthoclase, and muscovite, in decreasing order of abundance (Feitler 1967). Mined only in North Carolina, it is a major source of feldspar production in the United States. Alaskite occurs in three principal areas, referred to as the Spruce Pine, Penland, and Crabtree alaskite bodies, which are located, respectively, in Mitchell, Avery, and Yancey counties, North Carolina (Olson 1944). The largest mass of alaskite is between Spruce Pine and Chalk Mountain in Mitchell County. A 1981 mineral analysis of Spruce Pine alaskite showed 42.9% sodium (sodic plagioclase) feldspar, 28% quartz, 14.7% potassium feldspar (microcline, generally perthitic), 7.5% muscovite, 6.4% calcium feldspar, and small amounts of iron minerals and garnet. A corresponding average chemical composition of alaskite was SiO2, 74.4%; Al2O3, 15.4%; Fe2O3, 0.4%; CaO, 0.9%; K2O, 3.4%; Na2O, 5.1%; and LOI (loss on ignition), 0.4% (Redeker 1981). A 2004 analysis of Spruce Pine alaskite generally had the following mineral composition: 35% sodium feldspar (sodic plagioclase), 25% quartz, 30% potassium feldspar, 6% muscovite, and 4% calcium feldspar (A. Glover, personal communication). For comparison, an average chemical composition for granite was given as SiO2, 70.2%; Al2O3, 14.5%; Fe2O3, 1.6%; FeO, 1.8%; CaO, 2.0%; K2O, 4.1%; Na2O, 3.5%; and small amounts of other components (Reed 2004). Historically, in this region of North Carolina, pegmatites containing large amounts of microcline are thick (about 8 to 46 m) and occur near the abundant alaskite extending along the southeast side of the district from near Ingalls through Spruce Pine to the Crabtree Creek area. Prior to 1940, all the feldspar was mined from pegmatites by hand, but since 1940, the commercial production of feldspar has been revolutionized by feldspar flotation. Alaskite 455 Table 8. Theoretical end-member compositions of the principal feldspars, % Type K 2O Na2O CaO Al2O3 SiO2 Microcline 16.9 0 0 18.4 64.7 Orthoclase 16.9 0 0 18.4 64.7 Albite 0 11.8 0 19.4 68.8 Anorthite 0 0 20.1 36.6 43.3 replaced pegmatites as a source of raw material because bodies of alaskite are larger than the pegmatites. Also, compositional and mineralogical uniformity are greater, making the alaskite a more desirable flotation feed (Brobst 1962). Aplite Aplite is defined as a light-colored igneous rock consisting essentially of quartz, potassium feldspar, and sodic plagioclase (Jackson 1997). Commercial aplite mined near the Piney River area in Virginia until 1980 was identified previously as a pegmatite, a syenite, and Roseland anorthosite (Brown 1962). A description of rock from the same locality (Castle and Gillson 1960) suggests that the rock originally contained very coarse feldspar, which was subsequently granulated to give it a marked variability in texture. Aplite mined from Hanover County, Virginia, is the one current (2003) source of commercial production. The deposit is part of the Montpelier metanorthosite where rock is mined by U.S. Silica Co. (formerly by The Feldspar Corp.) at a quarry near Montpelier, Virginia (Bice and Clement 1982; Clement and Bice 1982). The metanorthosite intruded the Sabot gneiss and consists of two phases: a coarsegrained, gray, nonfoliated phase and a granulated, medium-grained foliated phase. The coarse-grained phase contains plagioclase crystals up to 25 to 35 cm that constitute 85% to 90% of the total rock. Feldspar-Quartz Mixtures (Sands) Feldspar is an abundant constituent in modern sands of diverse origins (Pettijohn, Potter, and Siever 1973). These sands most commonly occur as beach sands, sand dunes, and river sands. River sands tend toward more feldspathic compositions than either dune or beach sands. Although relatively few petrographic analyses give a breakdown of feldspar varieties, a survey of those that do suggests that potassium feldspar (orthoclase, microcline) is most abundant, followed by sodium plagioclases and the calcium plagioclases. Feldspar-quartz mixtures currently make up part of the current feldspar market and have been a significant portion of the industry. A major part of this production comes from the feldspar-rich quartz sand deposits located in California, Idaho, and Oklahoma. Some feldspar-quartz mixtures are a coproduct from feldspar flotation operations. The primary active California deposits are sandstone and deltaic deposits that contain quartz, and a range of 10% to 35% contained feldspar (Silva 1985). The Idaho deposit is a lacustrine (derived from a lake bed) sand with an estimated feldspar content of 30%. The Oklahoma operation processes an Arkansas River sand deposit containing 25% feldspar, of which about 72% is potassium feldspar (Bowdish 1978). In most cases, these silica deposits have been identified as extensive. Although they have not been developed thus far, the Kankakee dune sands in Kankakee County, Illinois, contain an average of about 21% feldspar. The sands are composed of quartz, plagioclase feldspars, potassium feldspar, mica, pyrite, and some other accessory minerals (Bhagwat et al. 2001). 456 Industrial Minerals and Rocks Granite Granite is a plutonic (igneous) rock that contains largely feldspar and quartz and in which the alkali feldspar/total feldspar ratio generally is restricted to the range of 65% to 90% (Jackson 1997). Granite is mined from only one state: Georgia has two granitic sources, which have been mined for feldspar for a number of years. The Shadydale granite, mined in Jasper County, has a chemical composition of 13.9% Al2O3, 0.9% CaO, 3.6% K2O, and 4.7% Na2O. The Siloam granite, mined in Greene County since 1980, is a porphyritic granite containing perthitic microcline—47% microcline, 25% plagioclase, 20% quartz, 3% perthite, and 5% biotite. Ore from the two mines is blended and processed in a plant to produce a potassiumgrade feldspar. Pegmatites Exceptionally coarse-grained igneous rocks, pegmatites have a composition similar to that of granite (Jackson 1997). Granitic pegmatites, widely distributed throughout the crystalline rock areas of the United States, occur in rocks of many geologic ages and are most abundant near the margins of granitic intrusions. Most of the important pegmatite districts are included in three broad geographic belts: • Appalachian Belt, which extends from Alabama to Maine • Rocky Mountain Belt, which encompasses Colorado, Idaho, Montana, New Mexico, South Dakota, Texas, Utah, and Wyoming • Western Belt, which covers Arizona, California, Nevada, Oregon, and Washington From about 1865 to 1991, pegmatites in the Middletown, Connecticut, area were mined almost continuously for feldspar and other minerals. Pegmatite occurrences in the Middletown Area have been recorded in the hundreds. These pegmatites are composed essentially of perthite, quartz, plagioclase, and muscovite. Approximately 42% of the pegmatites contain more than 40% plagioclase. The Middletown pegmatites are largely granitic in composition and form a vast resource of feldspar, quartz, and scrap mica. The relative abundance of potassium and sodium feldspar-rich pegmatites is not related to the formation in which the pegmatite occurs, but rather shows a regional pattern in which potassium feldspar-rich pegmatites are more numerous to the south (Stugard 1958). North Carolina pegmatites are located in the Kings Mountain Belt within the Shelby District covering Cleveland, southwestern Lincoln, and western Gaston counties. The area currently has one producing operation (Bundy and Carpenter 1969); the feldspar that is obtained is a by-product of mica production (in 2003 as a feldsparquartz mixture). At the south end of the district, a coarse-grained phase of the Cherryville quartz monzonite is mined for mica, feldspar, quartz, and kaolin. The coarse-grained granite is gradational into pegmatite and also is cut by pegmatite dikes. Depending on weathering, the total feldspar content ranges from 13% to 40%, and the potassium feldspar content ranges from 6% to 7% (Horton 1981). Lithium pegmatites are located northwest of Kings Mountain and the Bessemer City area and were mined until 1998. The average composition of the lithium pegmatites going to mill feed was 20% spodumene, 32% quartz, 27% albite, 14% microcline, 6% muscovite, and 1% trace minerals. The pegmatites are generally not zoned, and the fairly uniform grade of the crude ore allows recovery of feldspar and mica by-products (Kesler 1976). Feldspathic sand was recovered as a by-product from lithium production until 1998, when the last spodumene mine was closed. The pegmatites of the Black Hills, South Dakota, occur in two main areas. The Harney Peak area encompasses the Keystone Dis- trict in Pennington and Custer counties, the Hill City District in Pennington County, and the Custer District in Custer County. The second area is the Tinton District in Lawrence County. Although the greater part of the pegmatite-bearing area is in Custer County, the Keystone District has a record of significant mineral production from pegmatites. The most abundant minerals of the South Dakota pegmatites are plagioclase feldspars (oligoclase and albite), potassium feldspars (perthite and microcline), and quartz. The minerals are uniformly distributed in many pegmatites, but in others they tend to be concentrated in specific structural units. South Dakota pegmatites have been classified on the basis of mineral distribution, texture, and their structural relationships to the wall rocks (Page 1953; Norton 1964). The following gives detailed descriptions of other feldspar occurences: • Barium feldspars have mineral structures very similar to those of potassium feldspars but are rather rare and are not being mined commercially. Barium feldspar with more than 90% of the BaAl2Si2O8 molecule is described as celsian (Deer, Howie, and Zussman 2001). Occurrences of barium feldspar have been reported in Australia, Italy, Japan, Namibia, Sweden, Wales, the United States, and a few other countries (Mineralogy Database 2005). • Amazonite is a gem variety of microcline feldspar and often is polished as a cabochon (i.e., cut so the top of the gemstone forms a convex surface). It displays a Schiller of light, which is a lustrous reflection, also known as iridescence. Amazonite is usually light green to blue green and is found in Australia, Brazil, Namibia, Russia, the United States, and Zimbabwe (Bernardine Fine Art Jewelry 2004). • Labradorite is plagioclase feldspar. Although much of the stone is dark gray, a Schiller effect can produce blue, green, gold, and yellow iridescent colors. Slabs of labradorite rocks are available in very large sizes, suitable for facings of office buildings. The material also is cut into cabochons. Labradorite is found in Australia, Finland, Labrador, Madagascar, the United States, and other countries (Arem 1987). • Moonstone refers to a feldspar of widely varying composition and from a wide variety of localities. For example, moonstone from Burma and Sri Lanka displays a white to blue sheen. • Sunstone is oligoclase or labradorite that contains hematite (Fe2O3) or goethite (Fe2O3•H2O) and inclusions of silicate or clay minerals, which reflect light and create a sparkling sheen in gold to brown color shades. Sunstone is found in Australia, Canada, India, Norway, Russia, and the United States (Arem 1987). TECHNOLOGY Commercial feldspar mining in the United States includes mining of feldspathic sand deposits and of hard-rock material such as alaskite. Dredging of river sand occurs at one operation in Oklahoma. In general, after mining of sand deposits or dredging of sand, processing steps can include washing, screening, classifying, leaching to remove surface stains, flotation, and drying. The Spruce Pine alaskite has been a major ore source since the mid-1940s, and a description of a typical alaskite feldspar operation that employs differential froth flotation for the recovery of a pure feldspar product follows. Mining Hard-rock mining is done by open-pit methods, either by the mine owner or by contractors. Stripping ratios are nominal, less than 1:1. Feldspars 457 –200 Mesh Slimes Trommel Screen 20 Mesh Reagents A V-Box Rod Mill Reagents B Reagents C Trommel Screen Feldspar Flotation 24 Mesh Mica Flotation Conditioner Mica Cleaner Flotation Stockpile ¾-in. Ore Waste to Dump or Reprocessing Iron Flotation Quartz Cleaner Flotation Trommel Screen 80 Mesh Drain Bins or Filters Dryer Dryers Hammer Mill Magnetic Separator Dry Ground Mica Pebble Mill Glass Feldspar Glass Quartz Pottery Feldspar Courtesy of Minerals Research Laboratory, North Carolina State University. Figure 1. Typical flowsheet for feldspar production with alaskite ore After the feldspar ore is drilled and blasted, secondary breakage is with a conventional drop ball. Ore is then loaded with a hydraulic shovel onto trucks and hauled to the crushing plant, which is adjacent to the flotation plant. Processing Figure 1 is a simplified flowsheet of a typical feldspar flotation plant and is intended to acquaint the reader with the concepts involved in feldspar production. Primary crushing is done with a jaw crusher in open circuit. Secondary crushing is with a standard or shorthead gyratory crusher in two or three stages, sometimes in closed circuit with a screen. The final crushed product is –25 mm (–1 in.). Grinding is normally done with rod mills in order to minimize slime generation, although one company uses ball mills without any apparent ill effects. The grinding mills are normally operated in closed circuit with a classifier in order to maximize grinding capacity. Although the feldspar mineral grains are liberated at 850 µm (20 mesh) or larger, grinding is usually carried out to –600 µm (–30 mesh) in order to optimize the efficiency of subsequent flotation steps. To reduce reagent consumption and produce a higher grade product, the feed to flotation must be sized to eliminate the slimes or –38 µm (–400 mesh) material. The fact that container glass customers prefer a +75 µm (+200 mesh) product is also a factor. Desliming is normally done with hydrocyclones. Once the feldspar feed is properly sized, the differential flotation process can begin. All the unit operations after crushing are operated in a continuous circuit, 24 hours a day, 5 days per week. The first flotation step is to remove mica, which later can be sold as a coproduct. Mica flotation is achieved by conditioning with a cationic collector (an amine) at pH 3 using sulfuric acid. The mica is removed in a froth product and is usually cleaned once prior to being dewatered and sold. Iron-bearing minerals such as garnet and ilmenite are removed next, this time using an anionic collector, petroleum sulfonate, again at pH 3. The iron-bearing minerals are collected in the froth product and pumped to tailings. The previous unit operations of grinding, sizing, mica flotation, and iron flotation have produced an essentially pure mixture of feldspar and quartz. Some of the traditional feldspar producers are marketing or have marketed this mixture for ceramic use under various trade names such as Minsilspar and Silospar. The product is filtered, dried, and cleaned with high-intensity magnetic separation or dry ground and sold, usually in bulk. Other company products are shown in Table 2. The production of a high-grade feldspar product requires a third flotation step, again at pH 3. The collector is the same cationic amine as used in mica flotation, but this time the pH is controlled with hydrofluoric acid to depress the quartz. The fluorine ion is a powerful depressant in the quartz-feldspar separation. A feldspar product is produced with good recovery in a single rougher flotation step. The feldspar-containing froth product is filtered, dried, and, if necessary, cleaned with high-intensity magnetic separation and stored in bulk prior to sales. A particular plant generally will produce several different products, all with the same chemistry (because of the same source rock), but with different physical specifications. For ground feldspar for ceramic and filler use, the dried flotation product is ground in a ceramic-lined ball mill in closed circuit with air classifiers to produce a –74-µm (–200-mesh) or a –44-µm (–325-mesh) product. As can be seen in Figure 2, this step is one of the more expensive unit operations in the whole processing scheme, and the ground feldspar commands a higher price. While feldspar producers strive to sell as high a percentage of the ore as possible, tailings (i.e., waste residue left from the processing of feldspar ore) inevitably account for 30% to 40% of the head feed. Tailings are dewatered in settling ponds, by filtration, or in tailings plants. Solid material generally is sent to a landfill, although some could be used as fill material in, for example, mine excavations (A. Glover, personal communication). Figure 2 shows the relative costs of the various unit operations as compared to the total cost of producing feldspar. The data have been derived by using cost experience for the various unit operations and costs that 458 Industrial Minerals and Rocks 100 Percentage of Total Costs Cumulative Percentage 20 80 15 60 10 40 5 20 0 0 Mining Grinding Crushing Figure 2. Table 9. Year Cumulative Percentage Percentage of Total Costs 25 Drying Flotation Bulk Loading Dry Grinding Tailings Bag and Load Administration Distribution of feldspar production costs Feldspar sold by U.S. producers, by use Glass* Ceramic and Other Total† Quantity, Value, kt thousand $ Quantity, Value, kt thousand $ Quantity, Value, kt thousand $ 1980 367 12,700 278 13,600 644 1985 353 15,600 285 16,400 638 26,300 32,000 1990 340‡ 17,900 260‡ 16,200 600 34,100 1995§ 570‡ 27,000 260‡ 18,900 830‡ 45,900 2000 520‡ 26,700 270‡ 19,200 790‡ 46,000 2003 560‡ 29,000 240‡ 16,000 800‡ 46,000 Source: USBM 1981–1996; USGS 1997–2005. * Includes container glass, fiberglass, and other glass. † Data may not add to totals shown because of independent rounding. ‡ Data rounded to no more than two significant figures because of partially estimated data. § Beginning in 1992, aplite data are included. have been published in cost-estimating manuals (Kauffman and Van Dyk 1994; A. Glover, personal communication). MARKETING Uses In the United States, feldspar for glass manufacturing is usually ground to 850 µm (20 mesh) to 425 µm (40 mesh) and contains 4% to 6% K2O; 5% to 7% Na2O; approximately 19% Al2O3; and 0.08% Fe2O3. Pottery-grade feldspar for whiteware and similar ceramic products usually ranges from 5% to 14% in K2O and is ground to 75 µm (200 mesh) with Fe2O3 content in the 0.07% range (Potter 1993). Table 9 shows the consumption of feldspar by major end-use markets from 1980 to 2003. Until 1991, glass (including containers, fiberglass, and other glass) accounted for more than half of consumption. Beginning in 1992, aplite was included in U.S. feldspar statistics, and, because aplite is largely used for glass, glass increased to about 65% to 70% of consumption. Ceramic and other uses were about 40% to 45% of feldspar consumption until 1991 and then decreased to about 30% to 35% thereafter. Glass Glass manufacturing is complex and encompasses an enormous range of compositions and product types. Materials for glassmak- ing can be classified in three groups: glass formers, fluxes, and stabilizers. Glass formers are basic ingredients that can be melted and cooled into a glass, such as silica (quartz sand) (Elert 2005). Fluxes are oxides, including potassium oxide (K2O) and sodium oxide (Na2O), which are added to lower the melting temperature of a glass batch. Stabilizers, which can be oxides such as alumina (Al2O3) and calcium oxide, impart to the glass a high degree of resistance to physical and chemical attacks. In conjunction, the fluxes and stabilizers control the working characteristics of the glass-forming (Tooley 1984). Although alumina does not represent a large part of the composition of most glass, it is important because it increases the resistance of glass to chemical corrosion, improves the hardness and durability, and enhances the working characteristics of the glass (Pincus and Davies 1983). Feldspar provides both alkaline oxides (K2O and Na2O) for fluxing and alumina and calcium oxide as stabilizers. An important source of alumina for glassmaking, feldspar has a low iron and refractory mineral content, a low cost per unit of alumina, no volatile constituents, and no waste. The products usually melt between 1,100° and 1,200°C and dissolve readily in the glassmaking batch. A typical batch for container glass contains about 8% feldspar, and a batch for glass fiber insulation contains about 18% (Roskill Information Services Ltd. 2002). The consumption and selection of glass raw materials are influenced significantly by the economics of the glass-manufacturing process and the glass product market. Therefore, specifications for raw materials vary based on particular circumstances and economics. However, raw materials for the glass industry require rigid physical and chemical specifications. Ceramics Ceramic and pottery products are the second largest consumer of feldspar products in the United States. The ceramic products generally consist of ceramic glazes, ceramic tile, dinnerware, electrical porcelain, and sanitary ware. Feldspars are used in the fine ceramic industry as a flux to form a glassy phase in bodies, thus promoting vitrification and translucency. They also are used as a source of alkalies and alumina in glazes. Feldspars also provide one of the few sources of waterinsoluble alkali compounds (Norton 1970). Consumption of feldspar varies depending on the finished product. Dinnerware and various china products may contain 17% to 20% feldspar; floor tile, 55% to 60%; high-tension electrical porcelains, 25% to 35%; kitchen and ovenware, 10%; vitrified plumbing fixtures, 25%; wall tile, 0% to 11%; and other special ceramic products, including dental porcelain, may require 60% to 80% feldspar (Singer and Singer 1963). The selection of a potassium versus a sodium feldspar for ceramic applications has been the subject of many investigations (Norton 1970). Feldspar fluxing differences also have been studied (Weinstein 1985) for deformation and the effect of the alkali type in feldspars on the glassy phase formed. Fillers Feldspar use as a functional filler and extender in the paint, plastic, rubber, and sealants industries has evolved in recent times as an application that improves product performance. In these uses, feldspar competes with other minerals and nepheline syenite and requires increased levels of research and technical marketing efforts. Feldspar products developed for these markets must comply with the following specifications: dry brightness, oil absorption, Hegman grind, particle-size distribution, surface area, and bulk density. Feldspars Feldspar gives paints and coatings favorable properties such as low vehicle demand, which means that the feldspar is not demanding or taking up polymer (binder) out of the paint mixture. Other opportune characteristics of feldspar are low viscosity at high pigment loading; high dry brightness and low tint strength; good film integrity; resistance to abrasion, chemical attack, and chalking (the formation of an easily crumbled powder on the surface of a paint film); excellent tint retention; and ease of dispersal. Compared to nepheline syenite, feldspar has exceptional resistance to frosting (whitening of a painted surface) but may exhibit slightly greater health hazards owing to the presence of free crystalline silica (Mommsen 1988; S. Robinson, personal communication). Product Pricing Published prices for feldspar can vary according to the application, particle size, quality, quantity purchased, source, and type of material. Therefore, price quotations serve only as a general guide. From 2000 to 2003, U.S. sodium feldspar prices have shown little or no increase. During the same time period, prices for potassium feldspar increased by about 10% to 30%. Published prices for U.S. ceramic-grade feldspar at year-end 2003, ex-works (i.e., cost, not including insurance or transport cost), bulk (not in bags), per metric ton, were about $66 to $83 for sodium feldspar and $138 for potassium feldspar. For glass-grade feldspar, prices were about $44 to $57 for sodium feldspar and $94 to $99 for potassium feldspar. Prices for Turkish sodium feldspar, f.o.b. Gulluk (i.e., free on board at Gulluk port), per metric ton, were $13 to $14 for crude, –10 mm, bulk; $75 to $80 for ground, –63 µm, bagged; and $54 to $56 for glass grade, –500 µm, bagged (Industrial Minerals 2003). Transportation Feldspar is shipped either in bulk or in 50-lb (23-kg) or larger bags. In the feldspathic minerals industry, the cost of transportation is often equal to the value of the material transported. In 2002, rail transport was still the dominant form of shipping. Rates generally were increasing 2.5% to 3% per year, and fuel surcharges were an additional 2% to 3%. With faster delivery and reasonable costs, truck transport was gaining market share (Rogers 2002). REGULATORY AND ENVIRONMENTAL CONSIDERATIONS In the United States, because of its crystalline silica (quartz) content, feldspar falls under the Occupational Safety and Health Administration’s Hazard Communication Standards, 29 CFR Section 1900.1200. The standard requires labeling and other forms of warning, material safety data sheets, and employee training for products containing identified carcinogens with concentrations greater than 0.1%. OUTLOOK The container glass industry, a major end user of feldspar, continues to face strong competition from other forms of packaging, such as metal, paper, and plastic containers. Use of recycled glass containers (as cullet) in glassmaking decreases consumption of mineral raw materials, including feldspar. Government legislation and regulation are also providing momentum for increased use of recycled glass (Roskill Information Services Ltd. 2002). With escalating production costs and resistance to price increases by consumers, feldspar producers will continue to face a challenging business environment for the foreseeable future (Rogers 2002). Beer and wine packaging is probably the single largest market for container glass in the world. Countries with large beer industries—including Brazil, the Czech Republic, Germany, Japan, Mex- 459 ico, the Netherlands, Poland, Russia, Spain, the United Kingdom, and the United States—have substantial glass production capacity. In the immediate future, the fastest-growing markets for container glass are projected to be in Asia and Latin America, where countries have fast-growing populations. At present, glass packaging is said to have a cost advantage over aluminum and plastic containers in most of these countries. For example, the Chinese and Indian container-glass markets are potentially very large (Roskill Information Services Ltd. 2002). The strong U.S. market in 2003 for new home construction and remodeling consumed about 267 million m2 of tile. Imports supplied about 78% of this demand with Italy providing 34% and Spain 17%. Consumption of porcelain tile continued to grow, partly because of its durability. Also, demand is increasing for larger-sized tiles, in sizes ranging from about 30 cm × 30 cm (12 in. × 12 in.) to 51 cm × 51 cm (20 in. × 20 in.) (Ceramic Industry 2004). Although U.S. vitreous china sanitary-ware consumption data are not available, U.S. demand is increasingly being filled by imports. In 2004, Mexico and China were the largest U.S. suppliers, providing about 58% of imports. According to The Freedonia Group, Inc., U.S. demand for vitreous plumbing fixtures may remain flat for the next several years. Instead, regions outside the United States, such as Asia, Eastern Europe, and the Middle East, may provide growth opportunities (Grahl 2004; The Freedonia Group 2004). Demand for ceramic grades of feldspar is projected to remain relatively stronger than demand for glass grades. The main centers of ceramics production are China, Italy, Spain, Latin America, and Southeast Asia. These areas, and Chinese, Italian, and Spanish companies in particular, have been the major consumers of feldspar during the past 20 years and are projected to remain so in the immediate future (Roskill Information Services Ltd. 2002). ACKNOWLEDGMENT Much of the material in this chapter was taken from the Feldspars chapter by Roger A. Kauffman and Dean Van Dyk in 1994. REFERENCES Arem, J.E. 1987. Feldspars. Color Encyclopedia of Gemstones. 2nd edition. New York: Van Nostrand Reinhold. Avalon Ventures Ltd. 2004. Avalon to proceed with processing of bulk sample from Warren Township anorthosite project. Press release. http://www.avalonventures.com. Accessed June 2004. Bernardine Fine Art Jewelry. 2004. Amazonite information and description. http://www.bernardine.com/gemstones/amazonite. com. Accessed January 2005. Bhagwat, S.B., R.E. Hughes, J.M. Masters, and P.J. DeMaris. 2001. Feldspar and Quartz from the Dunes of Kankakee, Illinois: A Preliminary Feasibility Study. 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