Genthite and Talc Composition, Crystallization & Structure
Nickel silicates of uncertain composition. Genthite contains magnesium, Ni2Mg2Si3010.6H20(?); Garnierite, H2NiSi04(?). Amorphoua, earthy to slightly botryoidal structure. As incrustations. H. = 3-4. G. = 2.2-2.8. Earthy and dull luster. Color apple-green to white. Infusible. Difficultly decomposed by hydrochlorie acid, giving separated silica. In O. F. color the borax bead brown. In C. T. blaeken and give water. Genthite found with chromite at Texas, Lancaster County, Pennsylvania. Garnierite occurs in considerable amount, associated with serpentine and chromite, near Noumea, New Caledonia, and serves as an important ore of nickel.
Talc – Steatite and Soapstone
Composition. A magnesium silicate, H2Mg3(SiO3)4 = Silica 63.5, magnesia 31.7, water 4.8.
Crystallization. Monoclinic. Crystals rare. Usually tabular with rhombic or hexagonal outline.
Structure. Foliated massive; sometimes in radiating foliated groups. Also compact
Physical Properties Perfect basal cleavage. Thin folia somewhat flexible but not elastic. Sectile. H. = 1 (will make a mark on cloth). G. = 2.8. Pearly to greasy luster. Color apple-green, gray, white in soapstone often dark gray or green. Translucent to opaque. Greasy feel.
Tests. Difficultly fusible (5). Unattacked by acids. Characterized by its micaceous structure and cleavage, by its softness and greasy feel. To be distinguished from pyrophyllite by moistening a fragment with cobalt nitrate and heating intensely; talc will assume a pale violet color, pyrophyIlite a blue color.
Varieties. Foliated Talc. Light green or white, foliated, with a greasy feel.
Steatite or Soapstane. Massive, with fine granular to cryptocrystalline structure. Gray to dark green colors; often impure, through the presenee of such minerals as clorite, tremolite, mica, ete.
Pseudomvrphous. Is frequentIy pseudomorphous after such minerals as enstatite, pyroxene, amphibole, chrysolite, ete.
Occurrence. Talc is a mineral of secondary origin formed by the alteration of magnesium silicates, such as chrysolite, enstatite, pyroxene, amphibole, ete. Found at times in the igneous rocks, because of the alteration of such silicates, especially in peridotites and pyroxenites. Most characteristically found, however, in the metamorphic rocks, where it may form as soapstone, practically the entire rock-mass, or oeeur as a prominent constituent in the schistose rocks, as in talc-schist. In the United States, tale or soapstone quarries are to be found chiefly along the line of the Appalachian Mountains, the mineral being produced in Vermont, Massachusetts, Rhode lsland, New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, and Georgia. important deposits are located in St. Lawrence County, New York, where the talc occurs in the form of beds of schist interstratified with limestones. It is associated here with tremolite and enstatite, from masses of which it has evidently been derived. Large deposits of soapstone occur in Virginia in a narrow belt running from Nelson County northeast into Albemarle County. It occurs here in sheets sometimes 100 or more feet in thickness. There is a long series of tale and soapstone deposits in Vermont, located along the east side of the Creen Mountains. Tale has been mined in considerable quantity in Swain County, North Carolina; also from California.
Use. In the form of slabs, soapstone is used extensively for wash tubs, sinks, table tops, electrical switchboards, hearthstones, furnace linings, etc. An especially compact variety is used for the tips of gas burners, for tailors' chalk, slate pencils, by the Chinese for carvings, etc. Talc is also used in a finely powdered form as a filler to give weight to paper, as a lubricant, for toilet powders, in paints, as a heat insulator, ete.
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