BUILDING AND ORNAMENTAL STONES. 361 



the eastern slope of Grassy Hill. The material from near Franklin 

 Court-Honse is stated to be the best of any of the above. About 30 

 miles southwest from Richmond, at Chula, in Amelia County, there are 

 outcrops of soap-stone said to be of fine quality, and which in former 

 times were quite extensively operated by the Indians. They have been 

 re-opened within a few years, and the material is now in the market. 

 Specimens of the stone in the Museum collection are by no means pure 

 talc, but carry abundant long brownish fibers of some amphibolic min- 

 eral. 



B. SERPENTINE, OPLUCALCITE, VERD ANTIQUE MAtfiBLB. 



(1) COMPOSITION, ORIGIN, AND USES OF SERPENTINE. 



Serpentine is essentially a hydrous silicate of magnesia, consisting 

 when pure of nearly equal proportions of silica and magnesia with from 

 32 to 13 per cent, of water. The massive varieties quarried for archi- 

 tectural purposes are always more or less impure, containing frequently 

 from 10 to 12 per cent, of iron protoxides, together with varying quan- 

 tities of chrome iron (chromite), iron pyrites, hornblende, olivine, min- 

 erals of the pyroxene group, and the carbonates of lime and magnesia. 



The origin of serpentine rocks has long been a matter of dispute 

 among geologists. Recent investigations tend to show that in many 

 cases they result unmistakably from the alteration of igneous eruptive 

 rocks, especially the olivine bearing varieties, such as the peridotites 

 and gabbros. In the varities ophicalcite, consisting of intermingled 

 serpentine and calcite or dolomite, the serpentine is apparently in all 

 cases derived by a procees of hydration and decalcification from a 

 non-aluminous pyroxene. The theory long ably advocated by Dr. Hunt 

 to the effect that the serpentine occurring intercalated with beds of 

 schistose rocks and limestones resulted from metamorphism of silico- 

 magnesian sediments deposited by sea waters is now very generally 

 abandoned, and it is doubtful if the substance ever occurs as an ori- 

 ginal deposit even in the eozoonal forms, but is presumably always 

 secondary.* 



Serpentine is a soft, though somewhat tough, compact rock of vari- 

 able color, usually greenish, though often variously streaked and spotted 

 with yellow, yellowish green, brownish or more rarely red, its color de- 

 pending, according to Delesse,t upon the degree of oxidation under- 

 gone by the included ferruginous mineral. The name serpentine is 



* For further information on this point the reader is referred to such papers as 

 T. G. Bonney on the serpentine and associated rocks of the Lizard District. Quar. 

 Jour. Geol. Soc. of London, 1877, Vol. xxxiii, p. 11, p. 884, and on the serpentine and 

 associated rocks of the Ayrshire coast, same journal, 1878, Vol. xxxiv, p. 7G9. Also 

 T. S. Hunt on Geological History of Serpentine, Trans. Royal Soc. of Canada, Vol. i, 

 Sec. iv, p. 169, and Wadsworth's Lithological Studies; also Williams on Serpentine 

 of Syracuse, N. Y., Am. Jour. Sci., Aug. 1887. 



tZirkel, Petrography, Vol. I, p. 320. 



