More than 100 specimens belonging to the serpentine group have been investigated optically and by means of x-rays. Essentially all of the species now classed within the serpentine group can be referred to two main divisions, each of which shows slight modifications in the intensities of certain lines. The first division, which is referred to as the mineral serpentine, consists of varieties whose patterns are similar in atomic spacing to that of serpentine, best represented by patterns of chrysotile. The name chrysotile is reserved for serpentine occurring in veins and consisting of flexible fibers. The second division, which is referred to as the mineral antigorite, consists of varieties whose patterns are similar in atomic spacing to that of antigorite, from Antigorio valley, Piedmont.

Fragments from the specimens of each division have been examined by the immersion method and their optical properties noted. Nearly all of the specimens have been studied in thin section. The fundamental structures of both divisions appear to be fibrous. From the x-ray and optical studies it appears that the matrix of chrysotile is serpentine and not antigorite as thought by some authors.

General comparisons have been made between chemical analyses compiled from the literature. Based on the results of the x-ray and optical studies and the chemical discussion it is proposed to drop the names schweizerite, metaxite, pyroidesine, marmolite, retinalite, thermophyllite, bastite and vorhauserite as distinct mineral species in favor of the one term serpentine. Likewise it is proposed to drop the names picrosmine, picrolite, williamsite, bowenite, porcellophite, and baltimorite for the term antigorite. The term serpentinite is suggested for rocks composed of serpentine or antigorite or a mixture of both.

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