BUILDING AND ORNAMENTAL STONES. i)6l 



the eastern slope of Orassy ITill. The material fVoin near Franklin 

 Court-House is stated to be the best of any of the abov^e. Al)out 30 

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

 outcrops of soai^-stone said to be of tine quality, and which in former 

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

 re-oi)ened 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 abuiulant lonp^ brownish libers of some amphibolic min- 

 eral. 



B. SERPENTIXR, OPntCALCITE, VERDANTIQUE MArfP.LE. 



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



Serpentine is essentially a hy<lrous silicate of magnesia, consisting 

 when pure of nearly cijual proitortions of silica and magnesia with from 

 J 2 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 jier cent, of iron protoxides, together with varying quan- 

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

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



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

 among geologists, liecent 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 i)eridotites 

 and gabbros. In the varities ophicalcite, consisting of intermingled 

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

 cases derived by a i^rocees of hydration and decalcification from a 

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

 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 evar occurs as an ori- 

 ginal deposit even in the eflzoonal forms, but is presumablj^ .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 furtlior infoniiatiou on this point tlio niiuler is reforred to such i>apers as 

 T, G. Bonney on tlio scsrpoiitino and associated rocks of the Lizard District. Qii.ar. 

 Jonr. Gcol. Soo. of London, 1877, Vol. xxxiii, p. 11, p. 884, and on tho sorpc^ntinc and 

 as.sociatcd rocks of tlio Ayrshire coast, same journal, 1878, Vol. xxxiv, j). 7(>'J. Also 

 T. S. Hunt on Geological History of Scri)ontino, Trans. Royal Soc. of Canada, Vol. I, 

 Sec. IV, p. 10!), and Wadswor til's Litholoj^ical Studios; also Williams on Serpentine 

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



1 Zii'kel, Petrography, Vol. i, p. :520. 



