Geologic Features
Asbestos consists mostly of magnesium silicate minerals—chrysotile, anthophyllite, and crocidolite. The term asbestos covers all fibrous minerals with some tensile strength which are poor conductors and can be used for heat-protection. Like talc, they are derived principally from the alteration of olivine, pyroxene, and amphibole,—or more commonly from serpentine, which itself results from the alteration of these minerals. Chrysotile is the most common, and because of the length, fineness, and flexibility of its fibers, enabling it to be spun into asbestos ropes and fabrics, it is the most valuable. Anthophyllite fibers, on the other hand, are short, coarse, and brittle, and can be used only for lower-grade purposes. Crocidolite or blue asbestos is similar to chrysotile but somewhat inferior in fire-resisting qualities.
Asbestos deposits occur chiefly as veinlets in serpentine rock, which is itself the alteration of some earlier rock like peridotite. They are clearly formed in cracks and fissures through the agency of water, but whether the waters are hot or cold is not apparent. The veinlets have sometimes been interpreted as fillings of contraction cracks, but more probably are due to recrystallization of the serpentine, proceeding inward from the cracks. In Quebec the chrysotile asbestos (which is partly of spinning and partly of non-spinning grade) forms irregular veins of this nature in serpentine, the fiber making up 2 to 6 per cent of the rock.
In Georgia the asbestos, which is anthophyllite, occurs in lenticular masses in peridotite associated with gneiss. It is supposed to have formed by the alteration of olivine and pyroxene in the igneous rocks. In Arizona chrysotile is found in veins in cherty limestone, associated with diabase intrusives. Here it is believed to be an alteration product of diopside (lime-magnesia pyroxene) in a contact-metamorphic silicated zone.
Crocidolite is mined on a commercial scale only in Cape Colony, South Africa. The deposits occur in thin sedimentary layers interbedded with jaspers and ironstones. Their origin has not been worked out in detail.
The deposits of Russia, the Transvaal, Rhodesia, and Australia are of high-grade chrysotile, probably similar in origin to the Quebec deposits. The asbestos of Italy and Cyprus is anthophyllite, more like the Georgia material.
BARITE (BARYTES)
Economic Features
Barite is used chiefly as a material for paints. For this purpose it is employed both in the ground form and in the manufacture of lithopone, a widely used white paint consisting of barium sulphate and zinc sulphide. Ground barite is also used in certain kinds of rubber goods and in the making of heavy glazed paper. Lesser amounts go into the manufacture of barium chemicals, which are used in the preparation of hydrogen peroxide, in softening water, in tanning leather, and in a wide variety of other applications.
Germany is the world's principal producer of barite and has large reserves of high grade. Great Britain also has extensive deposits and produces perhaps one-fourth as much as Germany. France, Italy, Belgium, Austria-Hungary, and Spain produce smaller but significant amounts.
Before the war the United States imported from Germany nearly half the barite consumed in this country, and produced the remainder. Under the necessities of war times, adequate domestic supplies were developed and took care of nearly all the greatly increased demands. Production has come from fourteen states, the large producers being Georgia, Missouri, and Tennessee. During the war, also, an important movement of barite-consuming industries to the middle west took place, in order to utilize more readily and cheaply the domestic product. For this reason it is not expected that German barite will play as important a part as formerly in American markets,—although it can undoubtedly be put down on the Atlantic seaboard much more cheaply than domestic barite, which requires long rail hauls from southern and middle-western states.