56 PHYSICAL PROPERTIES OF MINERALS. 



5. Silky : like silk ; it is the result of a fibrous structure 

 Ex. fibrous carbonate of lime, fibrous gypsum, and man^ 

 fibrous minerals, more especially those which in other form 

 have a pearly luster. 



6. Adamantine : the luster of the diamond. When sub- 

 metallic, it is termed metallic-adamantine. Ex. some varie- 

 ties of white lead ore. 



b. The degrees of intensity are denominated as follows : 



1. Splendent : when the surface reflects light with great 

 brilliancy, and gives well defined images. Ex. Elba iron 

 ore, tin ore, some specimens of quartz and pyrites. 



2. Shining : when an image is produced, but not a well 

 denned image. Ex. calcareous spar, celestine. 



3. Glistening: when there is a general reflection from 

 the surface, but no image. Ex. talc, copper pyrites. 



4. Glimmering : when the reflection is very imperfect, 

 and apparently from points scattered over the surface. Ex. 

 flint, chalcedony. 



A mineral is said to be dull when there is a total absence 

 of luster. Ex. chalk. 



COLOR. 



In distinguishing minerals, both the external color and the 

 color of a surface that has been rubbed or scratched, are 

 observed. The latter is called the streak, and the powder 

 abraded, the streak-powder. 



The colors are either metallic or non-metallic. 



The metallic are named after some familiar metal, as 

 copper-red, bronze-yellow, brass-yellow, gold-yellow, steel- 

 gray, lead-gray, iron-gray. 



The non-metallic colors used in characterizing minerals, 

 are various shades of white, gray, black, blue, green, yellow, 

 red and brown. 



There are thus snow-white, reddish-white, greenish- white, 

 milk-white, yellowish-white ; 



Bluish-gray, smoke-gray, greenish-gray, pearl-gray, ash- 

 gray ; 



Velvet-black, greenish-black, bluish -black ; 



Azure-blue, violet-blue, sky-blue, Indigo-blue ; 



Emerald-green, olive-green, oil-green, grass-green, apple* 

 green, blackish-green, pistachio-green (yellowish) ; 



What is observed respecting color 1 



