1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 289 



needing' more study. It is mentioned here only on account of its bear- 

 ing upon the subject in hand. 



The writer has elsewhere noted' the efficacy of pressure and shearing 

 in the production of fibrous serpentine (as well as calcite). The fibrous 

 seri>entine used as asbestos occurs, however, under such conditions as 

 to i)reclude any such ])ossibility of origin. As is well known, this 

 mineral is found in what are simply cracks rather than true veins, with 

 fibers standing at right angles with the walls, and under such conditions 

 tliat any lateral movement on the part of the walls themselves was 

 simply impossible. The material is doubtless a reproduction on a large 

 scale of the process so frequently seen in thin sections, where olivines 

 and other magnesian silicates undergo serpentinizatiou. The remarks 

 made here have only a slight bearing upon this mineral. 



Resume. — The points brought out in this paper and the suggestions 

 advanced are (1) that a very considerable ijroportion of the mineral 

 ill commercial use, and labeled as asbestos in mineral cabinets, is in 

 reality anthophyllite,'^ and (2) that the fibrous structure in this case, 

 and that of the true asbestos as well, is due, in many instances at 

 least, to a ])rocess of shearing — is, in fact, an exaggerated form of the 

 process of nralitization. The fibers are drawn out along the plane of 

 the vertical axis only, the parting or line of separation between 

 individual fibers taking place mainly along cleavage lines, each one 

 being, therefore, an elongated prism bounded by cleavage faces, but 

 with form somewhat compressed or otherwise distorted by pressure. 

 Tlie broad faces on the fibers will therefore correspond to the faces of 

 the unit prism.^ The fact that the fibers do not in all cases run even 

 approximately parallel to the walls of the inclosing rock is not necessa- 

 rily opposed to the view. Owing to a lack of homogeneity in a rock 

 mass subjected to a compressive force, there may be developed at an 

 early stage, a series of short, step-like folds bordering closely upon, or 

 perhaps passing into faults, in which the materials forming the yielding 

 portion of the mass may be ground to powder, crimped, puckered, or 

 even rendered fissile, or fibrous, according to their individual qualities. 

 In such cases, the fibers may stand, relative to the inclosing, more 

 resisting rock masses, in all i^ositions short of at right angles. 



'On the Serpentine of Montville, New Jersey, Proc. U. S. Nat. Mus., XI, 1888, p. 105. 



-Penfield states (Am. Jour. Sci., XL, Nov., 1890, p. 394), in speaking of the occurrence 

 of anthophyllite, " Many specimens which may be seen in collections labeled 

 authophyllite will be found, when examined with the microscope, to be fine fibrous or 

 radiated varieties of hornblende." My own observations, as here noted, are quite 

 to the contrary, it being much more common to find fibrous anthophyllite labeled 

 asbestos than the reverse. 



^See description of Nahaut material, p. 285. 



Proc. N. M. 95 19 



