Vermont State Mineral
Talc is a hydrous silicate mineral composed of magnesium, silicon, oxygen, and water. Talc is relatively pure in composition but can contain small amounts of aluminum, iron, manganese, and titanium. Talc can be white, apple green, dark green, brown, gray, or colorless, depending on its composition.
Talc is the softest mineral, having a Mohs hardness of one, compared to diamond with a hardness of 10. Talc is composed of microscopic platelets, and the bonds holding the platelets together are very weak. This enables the platelets to slide by one another and results in talc’s soft and greasy feel.
Talc is also used as a term to describe a rock that contains the mineral talc. Other names for talc-rich rocks are steatite, a high-purity massive ore variety, and soapstone, an impure rock containing talc and other minerals.
Large talc deposits are found in Vermont. They were formed in ocean crust that was left after the continents collided. Depending on the year, the Green Mountain state is the second or third largest producer of talc in the United States. Talc and soapstone are associated minerals in the rocks of the Green Mountains. Talc is currently mined in Ludlow, Vermont. The state legislature designated talc the official mineral of Vermont in 1991.
The English word talc comes from a Persian word, which comes from the Arabic word talq.
FORMATION AND OCCURRENCE
Talc is formed by two processes. In the first process, heated waters carrying magnesium and silica in solution react with and replace beds of dolomitic marble. The second process for forming talc involves the alteration of igneous rocks that contain abundant, heavy minerals. A sequence of fluids reacts with these magnesium-rich minerals in the host rocks, ultimately replacing the minerals with talc. These talc deposits form as rinds on the igneous rock bodies or nearly completely replace them.
Talc is widespread. Some localities for good crystals or pure material are listed here.
Talc has been used by humans for centuries. The ancient Babylonians carved talc. The most commonly known use of talc today is in talcum, or "baby," powder. Soapstone is darker due to chlorite impurities and is used for sculpture as well as in manufacturing countertops and sinks.
High-quality pure talc is useful to the agriculture, housing, automotive, and other manufacturing industries for its softness, purity, fragrance retention, whiteness, luster, moisture content, oil and grease adsorption, chemical inertness, low electrical conductivity, high dielectric strength, and high thermal conductivity. U.S. talc is used in the production of ceramics, paint, paper, plastics, roofing, rubber, cosmetics, pharmaceuticals, adhesives, flooring, and caulking.
Several medical studies have been done in the past several decades on the association of talc and certain kinds of cancers, including cancers of the lung, ovaries, and skin. One study at Harvard Medical School showed that "perineal talc use may modestly increase the risk of invasive serous ovarian cancer."
Several organizations have petitioned the U.S. Food and Drug Administration (FDA) to add a warning label to cosmetic talc products. However, since no conclusive study has shown an association between talc and certain cancers, the issue continues to be disputed. Talc remains approved by the FDA for cosmetic use.
Pyrophyllite is a similar mineral with nearly identical physical properties to talc. Pyrophyllite is used as a substitute for talc in the manufacturing of ceramics. Kaolin, a clay mineral, and mica can be used in place of talc in many other manufacturing processes.
Chemical Formula: Mg3Si4O10(OH)2
Crystal Structure: Triclinic
Hardness (Mohs): 1
Color: Colorless, white, pale green, bright emerald-green to dark green, brown, gray
Luster: Greasy, pearly, dull
Density: 2.58-2.83 g/cm3
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press