496 REPORT OF NATIONAL MUSEUM, 1900. 



twinned unci frequently repeated, forming pseudo-hexagonal crystals 

 with or without reentrant angles. The cleavage of the mineral is 

 quite distinct in one direction. Fracture uneven. Its hardness is 8.5. 

 Specific gravit}'^ 3.5 to 3.84. Luster, vitreous. The color ranges from 

 asparagus green, grass green, emerald green, greenish white, yellowish 

 p-rcen, o-olden vellow, to brown and intermediate hues: sometimes a 

 rasp})erry or columbine red by transmitted light, and occasionall}'^ hav- 

 ing a bluish opalescence internally. 



Alexandrite is the emerald-green variety which b}' artificial light 

 appears a columbine or raspberry red. The crystals have a specific 

 gravity of 3.044. 



Cymophan6, or true cat's-e^^e, is of a greenish ^^ellow color and 

 exhibits a fine chatoj^ant effect, due to minute internal striations result- 

 ing from twinning, either of the crj^stal itself or of minute composite 

 crystals of which the whole is made up. 



The name chrysoheryl is from jpv goff, golden, and §r}pvXkoz^ beryl. 

 Cymoj^have, from KV}xa^ wave, and (jxxivco, to appear, alludes to its 

 peculiar opalescence. Alexandrite is named after Alexander 1 of 

 Russia. 



Chrysoberyl of gem value has not as yet been found in the United 

 States. "^I'he chief source of the supph'^ is Minas Geraes, Brazil, and 

 Ceylon. Alexandrite occurs chiefly in the Orenburg district, the Urals, 

 Siberia. 



CHRYSOCOLLA. 



This muieral, when coated with or contained in quartz or chalcedonj^ 

 is occasionally cut as a gem. Chrysocolla is a h^^drated copper silicate 

 having a mountain green, bluish green, passing into a sky blue, color. 



COAL. 



JET — CANNEL — ANTHRACITE — BROWN. 



The most important of the mineral coals used for ornamental pur- 

 poses is jet, a compact, soft, light coal of a lustrous velvet black color, 

 susceptible of a high polish. It is the Gagates of Dioscoridesand Pliny, 

 a name derived from the river Gagas, in S^'ria, near the mouth of 

 which it was early found. The finest specimens are now found in 

 detached pieces in a clay near Whitby, Yorkshire, England. 



Ccmnd coal has a dark gra_yish-l)lack or brownish-black color; a fine, 

 compact texture; a large conchoidal fracture, and receives a good pol- 

 ish. It burns readily, without melting, with a clear yellow flame, and 

 has l)een used as a substitute for candles, whence its name. It is occa- 

 sionally worked into inkstands, snuff boxes, breast pins, bracelets, 

 and other similar articles. 



AiifJirticite is harder than either jet or cannel coal; it is iron black 

 in coloi-; occasionally iridescent, and lias a bright, often submetallic, 

 luster, and a conchoidal fracture. Anthracite is sometimes made into 



