1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 287 



fibers were some 4 or 5 inches in length, of a green-brown color, silky- 

 luster, and great toughness. These also ran transversely to the walls 

 of the vein. The mineral was subsequently shown by Lacroix to be 

 monocliuic in crystallization, and hence treraolite, rather than antho- 

 phyllite, although tlie analysis as given' (No. 33) shows it to be very 

 low in lime. F. von Sandberger describes - asbestos and epidote, so 

 associated as to indicate that they result from the alteration of horn- 

 blende and augite, in South Tyrol, in Nassau near llof, and in Pribram. 



The above enumerated observations, it will be observed, throw little 

 light upon the subject, other than indicating that the mineral is a 

 secondary product after augite or hornblende. IMy own observations 

 in the field are limited to three localities, in all of which indications as 

 to the secondary nature of the mineral, as well as to the probable efticacy 

 of shearing, were unmistakable. These localities ;ire at the well-known 

 "soapstoiie" quarries of Alberene, in Albemarle County. Virginia, 

 and near Alberton, in Howard County, Maryland. 



The "soapstone" at the first-named locality is not a pure steatite, 

 but rather an admixture of various alteration products, among which 

 a colorless tremolite and light-green talc are most conspicuous.^ What 

 the original rock may have been is not apparent from a study of thin 

 sections, but the appearance in the field is such as to suggest it to have 

 been a i)yroxenite. It occurs in the form of a broad dike or sheet, 

 parallel and dipping with the gneiss ( ?) in which it is inclosed, and, as 

 dis^dayed in the quarry opening, is traversed by numerous irregular 

 veins of coarsely crystalline calcite. The rock is very massive, in gen- 

 eral appearance eminently suggestive of an eruptive pyroxenite which 

 has undergone extensive hydration and carbon atization, whereby a 

 considerable portion of its calcium has sei)arated out in the form of 

 calcite. As is almost invariably the case in rocks of this class, the 

 mass is traversed by numerous joint planes, some of which are pro- 

 nouncedly slickensided. Asbestos, as found, is always along these 

 slickeusided zoues, with fibers parallel to line of movement. The mate- 

 rial is, as a rule, in the form of thin plates or sheets, rarely over 10 mm. 

 in thickness, but perhaps several feet iu breadth, which bear every 

 evidence of compression, accompanied by a shearing movement whereby 

 the material is drawn out into a series of lamina' and the lamiiue 

 again into fibers. In one instance the material was fibrous (asbesti- 

 form) only where it had been subjected to a sharp crimi)ing ju-ocess, 

 such as would result from the impinging of the end of one block against 

 another at a considerable angle, accompanied by a slight lateral move- 

 ment. The physical and chemical properties of the fibrous mineral are 

 those of true asbestos (Analvsis 12). 



' Traus. Royal Society of Edinbiugli, XXVIII, 1877-78, p. 531. 



-Neues Jalirb. fiir Min., etc., 1888, I, pt. 3, p. 208. 



■'A chemical analysis of the stone, by K. L. Packard, yielded SiO.., 39.06 per ceut; 

 AlcOs, 12.84 per cent; FeO, 12.93 percent; CaO, 5.98 percent; MgO, 22.76 per ceut; 

 ignition, 6.56 per cent. Total, 100.13. All iron calculated as FeO. 



