240 DESCRIPTIONS OF MINERALS. 



cinth or fire-red reflections. It comes from Mexico and the 

 Faroe Islands. 



Common Opal, Semiopal. Common opal has the hardness 

 of opal and is easily scratched by quartz, a character which 

 distinguishes it from some siliceous stones often called semi- 

 opal. It has sometimes a milky opalescence, but does not 

 reflect a play of colors. The lustre is slightly resinous, and 

 the colors are white, gray, red, yellow, bluish, greenish to 

 dark grayish-green. Translucent to nearly opaque. Phillips 

 found nearly 8 per cent, of water in one specimen. 



Hydropliane. This variety is opaque white or yellowish 

 when dry, but becomes translucent and opalescent when 

 immersed in water. 



Cacholong. Opaque white, or bluish white, and usually 

 associated with chalcedony. Much of what is so called is 

 nothing but chalcedony; but other specimens contain water, 

 and are allied to hydrophane. It contains also a little alu- 

 mina and adheres to the tongue. It was first brought from 

 the river Oaoh in Bucharia. 



Hyalite, Midler's Glass. A glassy transparent variety, oc- 

 curring in small concretions and occasionally stalactitic. 

 It resembles somewhat a transparent gum arable. Composi- 

 tion, Silica 92-00, water 6*33 (Bucholz). 



Menilite. A brown opaque variety, in compact reniform 

 masses, occasionally slat} 7 . Composition, Silica 85*5, water 

 11*0 (Klaproth). It is found in slate at Menil Montant, 

 near Paris. 



Wood Opal. An impure opal, of a gray, brown or black 

 color, having the structure of wood, and looking much like 

 common silicified wood. It is wood petrified with a hy- 

 drated silica (or opal), instead of pure silica, and is distin- 

 guished by its lightuess and inferior hardness. Specific 

 gravity, 2. 



Oped Jasper. Resembles jasper in appearance, and con- 

 tains a few per cent, of iron ; but it is not so hard, owing to 

 the water it contains. 



Siliceous Sinter has often the composition of opal, though 

 sometimes simply quartz. The name is given to a loose, 

 porous siliceous rock usually of a grayish color. It is de- 

 posited, around the Geysers of Iceland and the Yellowstone 

 Park, in cellular or compact masses, sometimes in fibrous, 

 stalactitic, or cauliflower-like shapes. It is often called gey- 

 serite. Pearl sinter, or fiorite, occurs in volcanic tufa in 



