[Talc]
H₂Mg₃(SiO₃)₄
Occurs in scales, or in fibrous, scaly or compact masses; hardness, 1; specific gravity, 2.7; color white, gray or pale-green; luster pearly; translucent on thin edges.
This mineral is as soft as any, only graphite and molybdenite being of the same hardness, but both these latter two have a black streak, while the streak of talc is white. The greasy feel is also characteristic. Talc is very seldom found in crystals, but if they are found, they will appear like flakes and have a hexagonal cross section, though in reality they belong to the monoclinic system.
Talc is a secondary mineral which usually results from the exposure of magnesium silicates, such as pyroxenes or amphiboles, to moisture. In this case, in-as-much as the original rocks were metamorphic in origin, the talc therefrom will occur in old metamorphic regions. Some talc is also formed by the action of silica-bearing waters on dolomite. This is likely to be the case near the contact between dolomite and igneous rocks. Talc is closely related to serpentine and likely to be found in the same regions.
Talc has come to have a considerable use. Some of it is compact and then called soapstone, and this was used by the ancient Chinese to make images and ornaments; and our North American Indians used it to make large pots, to serve as containers for liquids. Some of these pots have been carved out with great skill, so as to be fairly light in proportion to what they would hold. Pipes and images were also carved from soapstone. Today we still cut soapstone into slabs to make mantels, laundry tubs and sinks. The scaly and fibrous varieties are ground, and used in making paper, paint, roofing, rubber, soap, crayons, toilet powders, etc. The United States produce and use over half the world’s production, our industries requiring over 100,000 tons of talc a year. Of this 38% goes into paper, 23% into paint, 18% into roofing, and so on down to toilet powder which uses 2½%, or 2,500 tons a year.
Talc is found in metamorphosed regions, that is in New England, all down the east side of the Appalachian Mts., in the Rocky Mts., and the Cascade Ranges, with a large number of local occurrences. New York State is the leading producer.
[Serpentine]
H₄Mg₃Si₂O₉
[Pl. 43]
Occurs in compact, granular or fibrous masses; hardness, 3; specific gravity, 2.6; color green; luster greasy; translucent on thin edges. Serpentine is never in crystals. Its color and hardness serve to distinguish it. Like talc it is a secondary mineral resulting from the alteration, in the presence of moisture, of pyroxenes, amphiboles, and especially, olivine. As these are often in metamorphic rocks, the serpentine is likely to be associated with metamorphic rocks. Some serpentine is also the result of the action of silica-bearing water on dolomite, and this is likely to occur in areas of sedimentary rocks. The fibrous variety of serpentine, chrysolite, usually occurs in seams or veins, and when the fibers are long, it is used as asbestos. This form of asbestos is the one most used commercially today, as there are remarkably large deposits of it in the Province of Quebec, which provide the major part of the world supply. In the United States it is also found in California and Arizona but only in moderate quantities.
Massive serpentine is used in considerable quantities as an ornamental stone, the green color varied with streaks and blotches of white, yellow and red, due to various impurities, making it very effective. It is, however, only suitable for interior work as the weather quickly spoils the polished surface. This is further discussed under serpentine rock, [page 245].
Serpentine is found at Newfane, Vt., Newburyport, Mass., Brewster, Antwerp, etc., N. Y., Hoboken, N. J., in Pennsylvania, Maryland, etc.