A large body of serpentinized basic rock bears, therefore, no certain promise of an asbestos supply, though it may offer encouragement for prospecting. High-grade fiber is evidently formed under a peculiar combination of geologic conditions which involve the presence of certain primary rock types, their alteration to secondary minerals and recrystallization of these in veins, such recrystallization being induced by a combination of metamorphic agencies. Although it is quite probable, therefore, that new fields will be discovered, there is no probability of an abundant supply.
An important point to be considered in connection with future supplies is that for most uses of asbestos there is little or no scrap recovery; that which is once used is for the most part gone beyond recall. It is wise, therefore, to maintain a conservative view of the asbestos reserve, for although there is evidence of a supply in the Canadian deposits and elsewhere to last for many years, the probability is that deposits of high-grade material are neither numerous nor extensive.
The total production and estimated reserves of spinning asbestos in the important producing countries are shown in [Figure 13].
Fig. 13.—Total production and estimated reserves of spinning asbestos.
GEOGRAPHICAL DISTRIBUTION
United States.
—Asbestos in the United States is of two types, chrysotile and anthophyllite. The chrysotile variety occurs in Arizona, Vermont, Wyoming, and California, and the anthophyllite in Georgia, Virginia, Maryland, Massachusetts, Connecticut, Rhode Island, and Idaho.
Chrysotile Asbestos.
—The asbestos deposits of Arizona are unusual in being cross-fiber chrysotile veins in cherty limestone, and thus quite distinct in origin from the Quebec deposits. The asbestos-bearing beds are thin and some of them are almost inaccessible.