INTRODUCTION

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.
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