274 DESCRIPTIVE MINERALOGY. 



Picrolitc, from Taherg in Sweden — Silica 40.98, magnesia 33.44, protoxide of iron 

 8.72, water 12.86, carbonic acid 1.73 {Lychndl). 



It may be here observed, that the crystalline forms of serpentine have usually been consi- 

 dered pscudomorphs ; and within a few years, M. Quernstedt has advanced the opinion that 

 they are pseudo-crystals of chrysolite, the peridot of Haiiy, and the prismatic chrysolite of 

 Mohs. One variety of this mineral, the olivine, occurs in lavas and in trap rocks and green- 

 stone ; a fact which accords sufBciently well with the occurrence of these serpentine crystals, 

 and of serpentine in the massive form, with or near the trappean or at least pyrogenous rocks. 

 Moreover, the composition of the olivine would offer no objection to this view. According to 

 Walmstadt, the olivine from Somma contains silica 40.08, magnesia 44.24, oxide of iron 

 15.26. But the strongest argument is the close similarity in the crystalline form. And the 

 change in composition to convert olivine into serpentine, being chiefly that of the removal of 

 oxide of iron and the substitution of magnesia, is not more remarkable than that which we 

 know to have taken place in hornblende, scapolite, spinelle, and several other minerals. This 

 view will moreover account for that want of perfection so marked in the crystals of serpentine. 



Uses. When compact, and susceptible of a polish, it is highly esteemed for ornamental 

 purposes. It may also be used for the preparation of some of the salts of magnesia. Soap- 

 stone, in consequence of its resisting the action of heat, is employed for lining furnaces, and 

 other similar purposes. It has also been used as a cheap paint. 



LOCALITIES. 



Serpentine, in its different varieties, is quite abundant in this State. I shall notice only the 

 more important localities. 



Essex County. The precious variety, often having a very rich green colour, is found asso- 

 ciated with white limestone in several parts of this county. In the immediate vicinity of Port 

 Henry, there are fine specimens, both massive, and disseminated in small grains or angular 

 fragments in the limestone, forming the verd-antique marble. Large blocks of this material 

 may be here obtained. It is susceptible of polish, and exhibits all the characters for which 

 the vcrd antique is so highly esteemed. 



. Jefferson County. In the town of Antwerp, two miles southwest of Oxbow, serpentine 

 Fig. 186. is found, which has a yellowish green colour, and is both massive and 



crystallized. It is in white limestone, and often has veins of amianthus 

 running through it. Granular plumbago ^also occurs in the limestone. 

 The crystals, although not entirely perfect, are much more so than is 

 usual in this mineral. Fig. 186 represents one of the forms, but it is not 

 easy to measure the inclination of the secondary faces. 



The massive variety at this locality sometimes has a slaty siructure, 

 and it is then also harder and more brittle. 

 Lewis County. Extensive beds of a dark and compact serpentine occur in the immediate 

 vicinity of Natural bridge. It sometimes passes into steatite, which is so soft as to be easily 



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