PRECIOUS STONES 339 



and of the poculiar sea blue of that rop;ion ; in one case the gen- 

 eral color was of the latter kind, clouded at ])oints with tlie 

 former — like the tint of a blue Alabashka topaz with included 

 clouds of Uralian amethyst. Both the purple and the sea 

 blue varieties at times pass into almost colorless fluor. That 

 received from Cavc-in-Rock presents an octahedral cleavage, 

 perfectly transparent and of amber yellow. A cubical crys- 

 tal received from Rosiclare was pale bluish, becoming nearly 

 colorless. 



Rock crj^stal is a variety of transparent colorless quartz, 

 composed of nearly pure silica. While it is not rare as a min- 

 eral, yet it is seldom found in masses of large size. When so 

 found, however, it is valuable for use in the ornamental arts. 

 One or two localities in the Alps, that have been known and 

 worked from Roman times, though very difhcult and perilous 

 of access, have furnished material for all the objects in Euro- 

 pean palaces and museimis which have been carvxd from this 

 substance. In Japan, too, large crystals were formerly ob- 

 tained, from which were made the polished balls so much priz- 

 ed by the natives, and afterwards by foreigners, who have 

 now almost drained the countr}^ of them by purchase. The 

 main supply in recent years has been derived from Madagas- 

 car and Brazil. 



Within the last decade ver}- fine rock crj^stal masses have 

 been obtained in the United States, especially in California. 

 An important discovery was made in 1891-92 b)^ Mr. James 

 Blackiston, near Placer\dlle, Eldorado county. 



The most remarkable discovery of quartz in California, 

 however, was made in 1897, in Calaveras county, at the old 

 Green Mountain mine, in Chile gulch, near Mokelumne Hill. 

 Here, in one of the ancient river channels filled with aurifer- 

 ous gravel and covered bj^ an overflow of lava — a formation 

 characteristic of that region of the state — was found a quan- 

 tity of enormous quartz crj^stals, imbedded in the old gravel. 



In Oregon, large transparent masses have been found near 

 Bay City, but no particulars of their occurrence are given. 



Some fine rock cr\^stal occurs in North Carolina, in Chest- 

 nut hill township, Ashe county, on a spur of Phoo'.iix moim- 

 tain, near Long Shoal creek. Here, at two or three spots not 



