What is Talc

Robert A. Clifton 1

What Is Talc?

REFERENCE: Clifton, R. A., "What Is Talc?" Definitions for Asbestos and Other Health-Related Silicates, ASTM STP 834, Benjamin Levadie, Ed., American Society for Testing and Materials, Philadelphia, 1984, pp. 158-174. ABSTRACT: Talc is a hydrated magnesium silicate produced by the metamorphosis of dolomite and quartzose rocks or by the hydrothermal alteration of ultramafic and mafic rocks. As the changes are rarely complete and uniform, the rocks usually contain one or more other minerals. In pure form it is the softest of minerals. Talc is an extremely useful and economically important mineral and is, like most materials, hazardous to a degree. This paper takes the position that talc is a victim. It is a victim of the imprecision of mineral terminology, which does not distinguish between the fibrous and nonfibrous varieties of several amphiboles. It is a victim of the terminology of its own industry, which sold "fibrous talc" for many years. It is victimized because precursor minerals in fibrous habit produce pseudomorphic talc fibers. Those same fibers are sometimes unaltered and present in talc in just enough quantity to give a near truth to claims that talc contains asbestos. Talc is a victim of monitoring methods that are totally nonspecific and call each elongate particle of whatever origin a fiber and, by analogy, asbestos. Most especially, talc is a victim of imprecise asbestos definitions, which allow the inclusion of most amphibole particles of some elongation in those definitions. KEY WORDS" health-related silicates, talc, asbestos, definitions

W h e n asbestos b e c a m e a cause o f serious e n v i r o n m e n t a l concern in the early 1970s, a s e g m e n t o f the talc industry p e r c e i v e d that the lack o f rigor in asbestos definitions posed an i m m e d i a t e threat to its o w n operations and a l o o m i n g threat to other segments o f the A m e r i c a n minerals industry. The U . S . Bureau o f M i n e s ( U S B M ) agreed with that assessment and has e x p e n d e d considerable effort in trying to assist the regulatory agencies in the use o f accurate mineralogical terms.2 In 1976 the U S B M established the Particulate M i n e r a l o g y U n i t to help clarify the confusion in particulate m i n e r a l o g y terminology, to d e v e l o p a solid scientific basis for research into particle-related pollution problems, and to p r o v i d e technical a d v i c e and assistance to regulatory bodies. The success o f these efforts can be j u d g e d in the light o f the need for such a publication as this. Quite a good e x a m p l e o f the abuses that grow out o f the misuse o f mineral terms can be found in the talc industry. l Physical scientist, Division of Industrial Minerals, U.S. Bureau of Mines, Washington, D.C. 20241. This paper does not address the question of the health hazards of fiberform talcs since it is against U.S. Bureau of Mines policy to evaluate health data. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 158 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

Copyright* 1984 by ASTM lntcrnational

www.astm.org

CLIFTON ON WHAT TALC IS

159

Definitions The following definitions are used for the term talc: 1. The pure mineral: (a) Mg6(SisO20(OH)4) [1]. 3 (b) 63.36% SiO2, 31.89% MgO, and 4.75% H20. (c) A soft p l a t y mineral. 2. A rock containing a mixture of hydrous magnesium minerals, with a composition ranging from pure talc to predominantly tremolite [2]. 3. Talcum, soapstone, steatite, potstone, and French chalk.

What Talc Is Talc is produced by the metamorphosis of dolomite and quartzose rocks or by the hydrothermal alteration of ultramafic and mafic rocks. As the changes are rarely complete and uniform, the rocks usually contain one or more of the minerals listed in Table 1 [3]. Note that both tremolite and anthophyllite can occur in fibrous forms and also that chrysotile is the fibrous form of serpentine. These associated minerals are a source of much trouble to the talc industry. Table 2 shows the variations in composition of the minerals associated with talc. The other names for talc need little explanation. Talcum, of course, is identified as the main ingredient of most cosmetic powders. Soapstone gets its name from its greasy feel, and the term is usually reserved for that less pure talc that is used for carving. Steatite is a more dense, purer talc, which can be machined, and the term includes its successor, the bonded, molded talc used in electronics. The term potstone refers to a use of talc during past millenia, even predating TABLE 1--Minerals that commonly occur in talc deposits. Mineral Group Carbonates Amphiboles Serpentines Other

Phase calcite dolomite magnesite tremolite~ anthophyllite~ antigorite chrysotile (uncommon) lizardite (uncommon) quartz mica, e.g., p h l o g o p i t e chlorite, e.g., penninite pyrophyllite

Formula CaCO3 CaMg(CO3)2 MgCO3 Ca2Mg~SisOzz(OH)2 (FeMg)TSisO22(OH)2

Mg3Si2Os(OH)4 Mg3Si2Os(OH)4 Mg3Si2Os(OH)4 SiOz Kz(Mg,Fe)6[Si6AI2020](OH)4 (Mg,Al,Fe)~2[(Si6AlsO20](OH)~6 AL[(SisO20](OH)4

"Occurring in fibrous and nonfibrous forms. Other trace phases are often present but are not included. 3 The italic numbers in brackets refer to the list of references appended to this paper. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

a10%

B203.

63 44 33 58 57 52 56 65 ... ...

Talc Serpentine (antigorite) Chlorite Anthophyllite Tremolite Actinolite Diopside Feldspar Magnesite Dolomite Calcite Quartz Muscovite M a g n e t i t e (Fe3Oi) I l m e n i t e (FeTiO4) Pyrite (FeS2) Tourmaline a Graphite ( 1 0 0 % carbon)

"36 .. .

I'~3 46 . . . .

SiO2

Mineral

. .

.

. .

. .

. .

. .

. .

CO2

. . . . . . . . . 2" .. . . 13 . . . 9 ... 26 . . . . . . . . . 52 30" 48 56 44 . . . . . . . . . . . . . . . . . . . . . . (Jr . . . . . . . . . . . .

. .

CaO

. .

. .

. .

. .

A1203

K20

Na20

. . . . . . . . . . . . . 18 . . . . . . . . . . . . . . . . . . . . . . . . . . 34 . . . . . . . . . . . . . . . . . . . . i8 17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "'" 39 10" 0.6 72 . . . . . . . . . . 33 . . . . . . . . . . 47 . 33 016 213 . . . . . . . . . . . . .

. .

Fe

2--Approximate composition of minerals present in talc ores, percent.

48" 22 ... . . 0.1 . . . . . . . . . . . 11 . . .

32 43 36 30 28 5 18

MgO

TABLE

. .

. .

. . . . . . . . . . .

3 8 5 15 15

7 13 14 2.2 2.3

3".8

4".3

to to to to to 3

H20

48~0

m

i--

m

m

_.~ "r"

"1" m

.-,., 9..

Z [~

.-.-I O

IxJ 1"1"1

-I1 O :l:l

Z

-I

9..

9"

"'"

9.. ...

TiO2

ID m

O

CLIFTON ON WHAT TALC IS

161

recorded history, when this mineral was carved to make cooking pots. Some talc is still sawed into handy pieces, and this "French chalk" is used for marking materials to be welded. Talc has been found very useful in many industries. The use of this unique material is enhanced by its low cost [a nominal $28 per metric ton ($25 per short ton) for crude ore in 1982]. The United States is the world's foremost producer and exporter of talc [4]. This mineral, produced from 35 mines in 11 states in 1981, was worth nearly $100 million, and the 1.1-million-metric-ton (1.2-million-ton) annual production is expected to double by the year 2000 [5]. Table 3 shows that resources in the United States are sufficient to permit this expansion, in the absence of serious environmental constraints. Figure 1 is a diagrammatic view of world talc supply and demand as of 1978. World production is on the left, sources of supply in the United States are in the middle, and the major end uses are on the right. The end uses served by ground talc (and hence its market distribution) are determined by its diverse properties, including its chemical and mineralogical composition, particle size and shape, specific gravity, hardness, and color. The largest use of talc is in the manufacture of ceramics--sagger bodies and other kiln furniture, sanitary ware, floor and wall tile, dinnerware, glazes, and electrical porcelains. In this application, the addition of talc to the usual claysilica-feldspar body mixtures facilitates the firing of the ware and improves the quality. The ceramic industry used 38% of the ground talc in the United States in 1981. Much of the talc used by the ceramic industry is a mixture of platy talc and blocky tremolite. The second major use of talc (21% in 1981) is as filler and pigment for paints. When used in paints, the platy varieties of talc have good hiding power, act as pigments in their own right, and serve to entangle and buoy up particles of other

TABLE 3 - - W o r l d

talc and related minerals resources, a in million short ton units, b

GeographicalArea

Reserves

Other

Total

North Ame~ca United States Other Total South America Europe Africa Asia and Oceania

150 10 160 5 60 5 100

600 40 640 20 190 20 400

750 50 800 25 250 25 500

330

1300"

1600

World total

"In collaborationwith the U.S. GeologicalSurvey. bl short ton = 0.9 metric tons. CThedata do not add to the total shown becauseof independent rounding. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

162

DEFINITIONS FOR ASBESTOS AND HEALTH-RELATED SILICATES

WORLDPRODUCTION I

t

BRAZIL265

] [

i

UNITED1,325STATES 2

I

FINLAND I 215

FRANCE 335

l

NORWAY [ 121E

ITALY

U.SSR 520E

]

-KOREA

165[

140E

]

[,

JAPAN 1,4~

I

IMPORTS ~.~ 19

I, 10 J iNDUSTRT STOCKS]

REPUBLIC OFKOREA 733

CHINA

I

I

193

L-ol INDIA 34O

"

1/1/78

210

J

1

AUSTRALIA 165 OTHER 368

I

!

WORLDTOTAL 6,475E

KEY E:ESTIMATEO SIC:STANOARG INDUSTRIACLASSI L FICATION

FIG. 1--Talc supply-demand relationships in the United States for 1978,

pigments, thus helping to keep them in suspension during prolonged storage. The properties of talc important to the paint industry are its color, fineness, oil absorption, chemical inertness, and optimum viscosity. The plastics industry, with its needs for both reinforcement materials and economic fillers, has recognized that talc satisfies both requirements, and the industry was the third largest user of talc minerals in 1981, with 11% of the ground talc market. Talc can be used as a filler or reinforcement or both, in both thermosetting and thermoplastic resins. It improves chemical and heat resistance, dimensional stability, stiffness, hardness, thermal conductivity, tensile strength, creep resistance, and electrical insulation. Talc also improves processability. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

CLIFTON ON WHAT TALC IS

163

CERAMICS [ 257 SIC3253,326

,NOU,,R,STOCK, ]

SIC2844

~ L]

EXPORTS 257

GOVERNMENT STOCKPILE RALANCE .................... 2 BLOCKANDLUMP.......... 1 GROUND ...................

CRUDE 106

I

87

1

PROCESSED j 1,030 I

I ~RO~.~YLLnE~ 113

13 SIC2879 PAINT 192 ] SIC2851 PAPER I

U.S.OEMAND

TALC 817

I

!

GROUNO 913 l .

SIC2621 PLASTICS 147 SIC2821 REFRACTORIESI 6 SIC3297 I ROOFING I 19 SIC3292 I RUBBER ] 36 SIC3069 "I OTHER 188

in 1000 short ton units (1000 short tons = 907 metric tons).

Fourth in order among the outlets for domestic talc minerals is its use for coating and loading of high-quality papers. In this application, high-purity talc helps in obtaining a product with the desired weight and opacity, good ink retention, and superior surface texture. A total of 9% of talc consumption went into the paper industry in 1981. Talc's ability to wet oil materials preferentially in the presence of water makes it a very effective pitch control agent in paper manufacturing. Another major use of minerals of the talc group is in agricultural chemicals used as carders or diluents for insecticides. Talc minerals are especially useful for this purpose because their chemical inertness makes them compatible with Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

164

DEFINITIONSFOR ASBESTOS AND HEALTH-RELATED SILICATES

a variety of toxic substances, while their physical characteristics facilitate the dispersion and increase the effectiveness of these agents. For roofing materials, including tar paper, asphalt shingles, and roll roofing, the addition of talc provides a surface that is nonsticking, chemically inert, fire retardant, and weather resistant. In cosmetic and pharmaceutical uses, talcs must be selected to meet the highest standards of purity, softness, pleasant feel, color, chemical stability, and freedom from any grit, irritants, or bacterial contamination. The use of talc minerals in refractories has much the same rationale as their use in ceramics. When used in rubber, talc minerals act as fillers, providing internal lubrication. They also serve as nonstick dusting agents. The remaining talc uses in the United States include such diverse minor applications as in agents for chemical warfare, floor waxes, shoe polishes, peanut polishing, and salami dusting. Somewhat more than one half of the total domestic output of talc is derived from open-pit operations, with the balance coming from underground mines. In both types of operations, the extraordinary slipperiness of talc ore imposes unusual traction problems in mine loading and hauling; in underground mines it also creates slippage problems in cribbing and timbering. Mining operations are usually carried out by conventional drilling and blasting methods. The softness of talc makes mining and processing easier than it is for most minerals. Selective mining and hand sorting are the methods most commonly resorted to for improving the quality of the output of crude talc-group minerals, but froth flotation is being employed increasingly to recover talc (Fig. 2) [6]. What Talc Is Not

Talc is certainly not asbestos, although it can be pseudomorphically fibrous. Not too many years have passed since talc producers were selling "fibrous" talcs under such names as Fibrene and Asbestine. In most of these so-called fibrous talcs, the fibrous component was hardly ever pseudomorphic talc, but was most often cleavage fragments of massive actinolite or tremolite. Sources of Real or Apparent Fibers

When talc crystallizes out of a solution of its components, as in the hydro~ thermal alteration previously mentioned, it is foliated or massive, the first two forms mentioned by Dana and Ford [7]. Pseudomorphic talc, the third form listed by Dana and Ford, is the only form for which those authors mention even apparent fibrosity. When metamorphosis occurs, the final mineral usually assumes the form of its predecessor. If a fibrous mineral were to be metamorphosed into talc, an apparent talc fiber would be created. Several industrial users of talc have been cited by the Occupational Safety and Health Administration (OSHA) for infractions of the asbestos regulations.

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CLIFTON ON WHAT TALC IS

TALCORE

.AWCFI.EFI ,,j

I

SCFIEE. ....,"1 I Undersize

I

I

Oversize

I ~Y"TDFIY~D~FI"I 1

'

I

ROTARYDRYER PEBBLEMILL

i i

"OL~FI'LL I

AIRCLeISSIFIER

II

A,.C~,E,EFI I

I

l

I

Coarse IIOOUDLE

I

l

I

I

Products

Rnes

DECKsSCREENI']

Oversize Unders~

Pred~'Is W~te

165

Oversize(top)

I

4,

[~,CE,~,AT.O TA.E~ ] I

I

I

I

Heavies

Overflow

1 ~DFIYEFI

I

J FROIHFLOTATIONi NickeI.Cob~1 Concentrate

(VERTICAU

I

Concen~ete

I

and Magnesite

Tailings

I T,,~

I

I

]

Products

.

.LTE~ 1

FIG. 2--Flowsheet of production by the Eastern Magnesia Talc Co. in Vermont.

OSHA based its findings on two observable facts: first, particles were found in the air that met the federal fiber criteria of equaling or exceeding an aspect ratio of 3 : 1 and being at least 5 t~m in length, and second, there was some tremolite also present in the air. There was no effort by the inspectors to demonstrate that the elongate particles were tremolite or that, if tremolite, they evolved from tremolite asbestos and not from the useful massive tremolite. The U S B M has long recognized the utility of the airborne fiber monitoring and control method developed by the British for use in their asbestos textile factories. It is a valid assumption that in that environment every elongate particle in the air bears a relationship to the asbestos in the air and that a diminution of their number would reduce the hazard. It is not valid in that, or any other, environment to assume that minerals can be identified by means of an optical

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166

DEFINITIONSFOR ASBESTOS AND HEALTH-RELATED SILICATES

microscope or to call every particle with a 3 : 1 aspect ratio either asbestos or a fiber and ascribe to it the demonstrated hazards of asbestos. The USBM finds itself today in full agreement with the conclusions of the National Bureau of Standards (NBS) in their 1977 report [8]. That report states that, after efforts to analyze the fiber content of 80 talc samples using the OSHA procedures, in their opinion the existing OSHA procedure was useful only for determining fiber content and not asbestos content; that the problem of the definition of asbestos remains; and that an acceptable resolution of that problem must precede development of acceptable measurement techniques and standards. The data in Table 4, taken from a study by Ampian [9], illustrate that those minerals that form in fibrous habit and are asbestos can have other forms and, in some cases, other names. Note that several of the minerals having the same chemical formula and (although not shown) identical crystal structures have both fibrous and nonfibrous analogs. Further, the habits ascribed to actinolite and tremolite could easily be found in nonasbestos elongate particles. Table 5, taken from Campbell et al [10], illustrates the semantic side of the problem. Mineralogists and the industry, fortunately, have given different names to the fibrous forms of serpentine, riebeckite, and cummingtonite-grunerite, but, unfortunately, they neglected to do so for anthophyllite, tremolite, and actinolite. This gives rise to such questions as "Is tremolite asbestos?" TABLE 4--Some fibrous and nonfibrous serpentines and amphibole minerals and varieties with their formulas. Mineral Serpentines Chrysotile Antigorite Lizardite J Amphiboles Anthophyllite

Formula

3MgO 9 2SIO2 9 2H20

4[(MgFe)TSisO2:(OH)2]

Actinolite), Tremolite J Amosite

4[(FEZ+Mg)TSisO22(OH)2]

Grunerite Cummingtonite Crocidolite

2[Fez+TSisO22(OH):] 2(MgFe2 +)7SisO22(OH)2 2 [Na2Fe23+(Fe~+Mg)3SisO22(OH)2]

Riebeckite

2[Na2Fe23+Fe32§

2[CadMgFe)sSisO22(OH)2]

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Form in Which It Appears fibrous and nonfibrous serpentines

fibrous and nonfibrous orthoamphiboles clinoamphiboles, often acicular and lath-shaped, rarely fibrous fibrous clinoamphibole derived from gruneritecummingtonite series with iron about 5.5, magnesium about 1.5 nonfibrous amphibole nonfibrous amphibole clinoamphibole, fibrous variety of riebeckite nonfibrous amphibole

CLIFTON ON WHAT TALC IS

167

TABLE 5--Asbestos and analog forms. Asbestos

Nonasbestos Analog

Chrysotile Crocidolite Amosite Anthophyllite asbestos Tremolite asbestos Actinolite asbestos

antigorite-lizardite riebeckite cummingtonite-grunerite anthophyllite tremolite Actinolite

Figure 3, taken from unpublished USBM research shows the X-ray diffraction pattern of a sample of tremolitic talc. The peaks identify three of the minerals present. The instrument, however, cannot differentiate between fibrous and nonfibrous minerals. The author has in his files a laboratory report, from a supposedly reputable commercial laboratory, saying that a sample from a talc mine contained 40% asbestos. Upon query, the laboratory admitted that they had not even made a petroscopic or microscopic examination and only quantified the tremolite peaks, calling them asbestos. Figure 4 from Campbell et al [10] is a photograph of a nearly pure tremolite rock. This is the form that by far the largest portion of that mineral takes upon formation. This form is obviously not, nor ever could be, asbestos. If, however, anyone were to crush or mill this rock, cleavage fragments could be produced, and such fragments might be "federal fibers," which would meet the regulatory agencies' definitions of asbestos without even coming close to being the true tremolite asbestos pictured in Fig. 5, also from Campbell et al [10]. Figure 6, excerpted from a recent National Toxicology Program draft manuscript, illustrates perfectly how nonfibrous material can become asbestos under the present definitions. The first two sentences, from the abstract, tell of the health effects. The amphibole group of minerals mentioned in Table 1 is the source of five of the asbestos minerals and is ubiquitous, occurring in much of the earth's crust and in most mining areas in the United States and elsewhere. The proclivity of this group of minerals to cleave (split) along definite, parallel, closely spaced planes makes certain that these minerals will produce "federal fibers" when crushed or ground. The amphiboles are present in practically all igneous-metamorphic rock terrain, and it is no coincidence, as shown in Fig. 7, that this terrain contains all of our talc mines. Figure 8, from Campbell et al [10], is about tremolite but is illustrative of all amphiboles. Note that more than 70% of the ground tremolite rock particles have Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

S31V0171S (]31V-I:II:I-HI"Iu

ONV 8 0 1 8 3 8 8 V

1:104 s

891,

~.nm

(1 -"4 C~

Z

r-

9~

ro

of m

7 7

~8 ~

--9 I-"

o m

t

4

_

,-I

Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

CLIFTON ON WHAT TALC IS

169

I

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170

DEFINITIONS FOR ASBESTOS AND HEALTH-RELATED SILICATES

/ L5

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CLIFTON ON WHAT TALC IS

171

Prel tminaPy bvtew

Trt~o 1tte

NI'? TECHNICALI~PORT ON THE CARCINOGENESISBIOASSAY OF TPJ[HOLITE NTP-82-gs NIH Publication No. 82U.S. DEPARTHENTOF h~ALTH AND HUMANSERVICES Public Health Servtco National Institutes of Health

Survival was c o , arable tn the t r m o l t t e and control groups. No toxtctty or increase in neoplasta was observed in the tromoltto exposed animals compared to the concurrent controls. Under the conditions of thts bfoassoy, conftbrous tron~lito was not toxic and did not cause s carcinogenic response Mien ingested at a level of 1~ in the dfet by male and female Fischer 344 rats for their ltfetfma, Crysta111ma tremollte

was

chosen for thts study because up to 20 years ago

I t ~S a common contaminant of tolc Milch was used tn foods and phamacouttcals. The grtndlng of trtqolttn In preparatlon for Its tntonded uso may result in the production of ftbers Mitch havo the Qorph010~ of L~bestos idnerals.

Stanton

(1981) in ravtewtog hts tntrapleural wlneral deposition sl~dtes speoulated that ~Az~ao the as~stos xtnoraljquestton my be ~lrectly related to ~lber slze So contrast to chemical ~ o s t t l o n .

Therefore, the s~d~ of crysUlltno ~emoltte ~ s

deemed spproprtate becouse~Ft~ri t s past vddespreod exposure a~d the fact that t t assumes fiber characteristics Mien ground in the processing of talc.

FIG. 6--Excerpt from a National Toxicology Program draft document.

a less than 3: 1 aspect ratio, while more than 40% of the particles from tremolite asbestos have an aspect ratio higher than 10: 1. A new ASTM standard, the ASTM Practice for Safety and Health Requirements Relating to Occupational Exposure to Asbestos (E 849-82), gives partial recognition to the inadequacies of previous definitions by defining fibers as monitored particles with an aspect ratio of at least 5:1, a minimum length of 5 Ixm, a maximum diameter of 3 txm, and the appearance of fascines, or bundles of sticks. Note that in Fig. 8 more than 70% of the milled tremolite asbestos would meet that criterion, while more than 90% of the milled tremolite rock would not. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

172

DEFINITIONSFOR ASBESTOS AND HEALTH-RELATED SILICATES

FIG. 7--Distribution of igneous metamorphic rock terrain (top) and talc deposits (bottom) in the United States.

Summary Talc is an extremely useful and economically important mineral. It is, like most materials, hazardous to some degree. 1. It is a victim of the imprecision of mineral terminology, which often has not distinguished between the fibrous and nonfibrous varieties of several amphiboles. 2. It is also a victim of the terminology of its own industry, which sold "fibrous talc" for many years. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

CLIFTON ON WHAT TALC IS

173

7~ 60

--.Tremolite --

---Tremolite

asbestos

"E r 0.

>: 40 z

14J (21 i,iJ tv14.

30

/ 20

/

lO

/

\ " ~

/

\

/ 1:1

\

~,,,~ 3:1

5:1

10:1

20:1

50:1

1 0 0 : 1 200:1

ASPECT RATIO FIG. 8--Particle size distribution of milled tremolite and tremolite asbestos.

3. Precursor minerals in talc in fibrous habit can yield pseudomorphic talc fibers. Those same fibers are sometimes unaltered and present in talc in just enough quantity to give a near truth to claims that talc contains asbestos. 4. Talc is a victim of monitoring methods that have often been nonspecific and have called each elongate particle of whatever origin a fiber and, by analogy, asbestos. 5. Most especially, talc is a victim of imprecise asbestos definitions, which allow the inclusion of most amphibole particles of some elongation in those definitions. Regulatory agencies should become more aware of the shortcomings of certain of their fiber measurement methods, including the identification of particle composition and crystalline habit by using methods such as electron diffraction and microscopy.

References [1 ] Deer, W. A., Howie, R. A., and Zussman, J., Rock-Forming Minerals, Wiley, New York, 1963. [2] Brobst, D. A. and Pratt, W. P., United States Mineral Resources, Geological Survey Professional Paper 820, U.S. Government Printing Office, Washington, D.C., 1973, pp. 619-626. Copyright by ASTM Int'l (all rights reserved); Sat Jun 23 13:42:11 EDT 2012 Downloaded/printed by Universidad De Antioquia pursuant to License Agreement. No further reproductions authorized.

174

DEFINITIONSFOR ASBESTOS AND HEALTH-RELATED SILICATES

[3] Rohl, A. N., Langer, A. M., Selikoff, I. J., Tordini, A., Klingentidis, R., Bowes, D. R., and Skinner, D. L., "Consumer Talcums and Powders: Mineral and Chemical Characterization," Journal of Toxicology and Environmental Health, Vol. 2, 1976, pp. 255-284. [4] Roe, L. A., "Talc and Pyrophyllite," Industrial Minerals and Rocks, 4th ed., S. J. Lefond, Ed., American Institute of Mining, Metallurgical, and Petroleum Engineers, New York, 1975, pp. 1127-1147. [5] Clifton, R. A., "Talc," Minerals Yearbook, Vol. 1, U.S. Bureau of Mines, U.S. Government Printing Office, Washington, D.C., 1982, pp. 827-832. [6] Clifton, R. A., "Talc: Mineral Facts and Problems," Bureau of Mines Bulletin, Vol. 671, 1980, p. 903. [7] Dana, E. S. and Ford, W. E., A Textbook of Mineralogy, 4th ed., Wiley, New York, 1960, pp. 667-678. [8] "A Report of the Fiber Content of Eighty Industrial Talc Samples Obtained From and Using the Procedures of the Occupational Safety and Health Administration (OSHA)." National Bureau of Standards, Washington, D.C., May 1977. [9] Ampian, S. G., "Asbestos Minerals and Their Nonashestos Analogs," paper presented at the Symposium on Electron Microscopy of Microfibers, Pennsylvania State University, University Park, Pa., 23-25 Aug. 1976 (available from S. Ampian, U.S. Bureau of Mines, Washington, D.C.). [10] Campbell, W. J., Blake, R. L., Brown, L. L., Cather, E. E., and Sjoberg, J. J., "Selected Silicate Minerals and Their Asbestiform Varieties: Mineralogical Definitions and IdentificationCharacterization," BuMines IC 8751, U.S. Bureau of Mines, Washington, D.C., 1977.

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