Talc
Current inventory:  0 gems
 

  
Talc is named from the Arabic word talq, for pure, probably alluding to the color of its powder.

Discovered in 1546;  IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Mg₃Si₄O₁₀(OH)₂

Magnesium Silicate Hydroxide

Molecular Weight:

379.27 gm

Composition:

Magnesium

19.23 %

Mg

31.88 %

MgO

Silicon

29.62 %

Si

63.37 %

SiO₂

Hydrogen

0.53 %

H

4.75 %

H₂O

Oxygen

50.62 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

SILICATES (Germanates)

Strunz 8th Ed. ID:

8/H.09-40

Nickel-Strunz 10th Ed. ID:

9.EC.05

9 : SILICATES (Germanates)
E : Phyllosilicates
C : Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

Related to:

Isostructural with Pyrophyllite-Talc Group. Talc Series.

Varieties:

Beaconite, Chromian Talc, Polyphant Stone, Pseudolite, Steatite

Synonyms:

Agalite, Asbestin, Colubrine, Federweiss, French Chalk, Gilstein, Lardite (of Wallerius), Lavezstein, Leberstein (of Haditsch & Maus), Mussolinite, Ollite, Talck, Yalck

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals platy, pseudotrigonal pyramids, to 1 cm; fibrous, fine-grained compact, massive

Twinning:

None

Physical Properties

Cleavage:

Perfect on [001]

Fracture:

Sub-Conchoidal

Tenacity:

Sectile; flexible but not elastic

Moh's Hardness:

1.0 (Mohs hardness reference species)

Density:

2.58 - 2.83 (g/cm³)

Luminescence:

Fluorescent; orange yellow under SW UV, yellow under LW UV (not always fluorescent)

Radioactivity:

Not Radioactive Thermal Behaviour: Stable to about 900 degrees Celsius.

Other:

Thermal Behaviour: Stable to about 900 degrees Celsius.

Optical Properties

Color:

Light to dark Green, Brown, White; Colorless in thin section

Transparency:

Translucent

Luster:

Pearly, Greasy, Dull

Refractive Index:

1.538 - 1.600  Biaxial ( - )

Birefringence:

0.0510

Dispersion:

Perceptible; r > v

Pleochroism:

Weak; only visible in dark varieties

Occurances

Geological Setting:

In talc-rich schists or steatite through hydrothermal alteration of mafic rocks (steatitization) subsequent to serpentinization during greenschist facies metamorphism. Also formed by thermal low-temperature metamorphism of siliceous dolostones.

Common Associations:

Actinolite, Tremolite, Chlorite, Pyroxene, Vermiculite, Serpentine, Anthophyllite, Dolomite, Calcite

Common Impurities:

Ni, Fe, Al, Ca, Na, H₂O

Type Locality:

Unknown

Year Discovered:

1546

View mineral photos:

Talc Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Talc is rarely thought of as a gem type mineral. However, it is an important industrial mineral that is has been used as a surface for lab counter tops and electrical switchboards due to its resistance to heat, electricity and acids. It is also an important filler material in paints, rubber and insecticides and in cosmetics as a lubricating dusting powder. Most people only know Talc as the primary ingredient in talcum powder. Mineral specimens are not very common since it does not usually form very large or attractive crystals. Faceted gems are very rare and difficult to cut due to the perfect cleavage and Mohs hardness of only 1.0 but can be attractive with their pale green translucence. Talc is a Mohs hardness reference mineral.

Distribution of Talc is of widespread occurrence. Some localities for good crystals or pure material include: on Mt. Greiner, Zillertal, Tirol, Austria. At Zermatt, Valais, and St. Gotthard, Ticino, Switzerland. From the Pfitschtal, Trentino-Alto Adige, Italy. At the Trimouns talc deposit, six km northeast of Luzenac, Ariμege, France. From Goepfersgruen, Bavaria, Germany. At Snarum, Norway. In the Onotosk deposit, Irkutsk, Siberia, Russia. In the USA, near Fowler, St. Lawrence County, New York; Delta, York County, Pennsylvania; Smithfield, Providence County, Rhode Island; Rochester, Windsor County, Vermont; Holly Springs, Cherokee County, Georgia; near San Andreas, Calaveras County, California.
 

  
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