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Vermont Symbols, Mineral: Talc
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Talc
Hydrous magnesium silicate
Mg3Si4O10(OH)2
Adopted in 1991.
Talc, the State Mineral, is metamorphic in origin, formed in thin slivers of ocean crust left here after the continents collided. Generally found in southwestern Vermont, it is green in color and very soft. In 1990, Vermont ranked second only to California among the states which produce talc. Ground talc is used in plastics, paper, rubber and paint.
Metamorphic in origin, formed in thin slivers of ocean crust left here after the continents collided. Generally found in southwestern Vermont, it is green in color and very soft. In 1990, Vermont ranked second only to California among the states which produce talc. Ground talc is used in plastics, paper, rubber and paint It is also used to coat products which need to slide apart easily, such as nested stacks of plastic pails in a hardware store! Soapstone, composed of chlorite and talc, can withstand intense heat and is used by some companies to make countertops and sinks. The Green Mountains are comprised of folded and faulted metasedimentary rocks, metamorphosed volcanic rocks and slivers of ocean crust (serpentinized ultramafic rocks). Talc, soapstone, and verde antique are associated with the ultramafic rocks. Talc is currently mined in the Ludlow area.
General Description:
Talc is one of the common minerals in metamorphic rock. Although talc deposits can be found throughout the world in various geological contexts, economically viable concentrations of talc are not that common. Abundant mostly on east side of Green mountains, near talcose slate, and found in a belt whole length of State. Marlborough, Windham county, known as “chalkstone;” Newfane, Chester, Grafton, and Athens, large quarries; also in Bridgewater, Plymouth, Cavendish, Weathersfield, Bethel, and Rochester, Windsor county; thence north in Washington, Lomoille, Franklin, and Orleans counties.
How talc deposits are formed
Talc deposits result from the transformation of existing rocks under the effect of hydro-thermal fluids carrying one or several of the components needed to form the mineral (MgO, SiO2, CO2). Tectonics play a major role in the genesis of a talc deposit. It enables hydro-thermal fluids to penetrate the rock, creating a micro-permeability that facilitates reactions in the mass. The size and shape of talc deposits depend upon the intensity of the hydrothermal activity which corresponds to the climate of a low temperature metamorphism. Pressure and deformations, both concurrent with and subsequent to this transformation, determine the crystallinity of the talc ore in the deposit.
Types of talc deposit
Talc deposits differ according to the parent rock from which they are derived. Four main categories exist.
Typical Physical Constants:
| Hegman Grind |
3- 6 |
| Density (g/cm3) |
2.7- 2.85 |
| Specific Gravity |
2.6- 2.85 |
| Oil Absorption |
30-55 |
| Melting Point (°C) |
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| Appearance |
White powder |
| Surface Area (m2/g) |
4.3 |
| Thermal Conductivity @20°C (cal/s-cm-°C) |
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| Mohs Hardness @20°C |
1.0- 1.5 |
| pH |
8.4-9.4 |
| Crystallography |
Lamellar |
| G.E. Brightness |
85- 93 |
| Refractive Index |
1.59- 1.60 |
From Office of the Secretary of State, Vermont Legislative Directory and State Manual, Biennial Session, 1993-1994, p. 25.
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