ORDER HI. HEXAHEDRAL 1'E ARL-KERATE. 155 



faintly streaked parallel to the edges of combi- 

 nation with the dodecahedron. 

 Lustre resinous, passing into adamantine. Faces 

 of fracture often more splendent than those of 

 crystallisation. Colour pearl-grey, passing on 

 one hand into lavender-blue and violet-blue, on 

 the other into greyish-, yellowish-, and greenish- 

 white, into siskin-green, asparagus-green, pista- 

 chio-green, and leek-green. The colour becomes 

 brown on being exposed to light. Streak shining. 

 Translucent... feebly translucent on the edges. 

 Sectile. Hardness = 1-0 ... 1-5. Sp. Gr. = 5-552, 

 a white granular variety from Peru. 

 Compound Varieties. In crusts: composition 

 scarcely observable, sometimes columnar. Mas- 

 sive : composition granular, strongly coherent, or 

 imperfect columnar, and often bent ; faces of com- 

 position rough. 



OBSERVATIONS. 



1. KLAPHOTH found two varieties of the present species, 

 one from Saxony, and the other from Peru, to consist of 



Silver 6775 76-0. 



Oxygen 6-?5 7'6. 



Muriatic Acid 14-75 16-4. 



Oxide of Iron 6-00 0-0. 



Alumina 1'75 0-0. 



Sulphuric Acid 0-25 0-0. 



The formula for its chemical composition is Ag M 2 , or 

 80-903 oxide of silver and 29-097 muriatic acid. It is fusible 

 in the flame of a candle, and emits fumes of muriatic acid. 

 Upon charcoal it may be almost entirely reduced before the 

 blowpipe, and is likewise easily reduced if rubbed wet upon 



