

OPTICAL CHARACTERS OF MINERALS. Ill 



7. Pinchbeck-brown. Yellowish-brown with a metallic lustre. 

 Ex. Talc, and Hypersthene. 



8. Wood-brown. Brown with yellow and much grey. The 

 color of old wood. Ex. Mountain wood. 



9. Liver -brown. Brown with grey and a little green. Ex. Com- 

 mon Jasper. 



10. Blackish-brown. Brown with much black. Ex. Bitumin- 

 ous coal. 



The colors above mentioned represent so many fixed points, be- 

 tween which there exist in nature numerous shades. These are 

 indicated by the two with which they best agree. If the color, in 

 a given case, differ but little from one of these standards, it is said to 

 be that color, only inclining or passing into another. 



Colors may be different in their intensity, though belonging to 

 one and the same variety. Differences of this kind are indicated by 

 the expressions pale, light, deep, dark, 



. 93. SERIES OF COLORS. 



The varieties of color occurring in the individuals of one 

 and the same species, form an uninterrupted series, which 

 is called the Series of Colors of that Species. 



All the species in mineralogy are not equally complete in this re- 

 spect. Many offer but few varieties of color, while others present 

 us with a very great number. In these last, it is observable, that 

 they insensibly pass into each other, or that every one of them is 

 intermediate between two others. Thus they represent an unin- 

 terrupted succession of the shades of colors, and give rise to what 

 is meant by the series of colors. 



The series of colors cannot be described ; they must be studied 

 from nature. An idea of them, however, is soon, and very easily 

 obtained by the examination of a few species very complete in this 

 particular, and which are arranged expressly for this end. The fol- 

 lowing are among the most eligible for the purpose ; Quartz, Tour- 

 maline, Mica, Fluor, Corundum, and Spinelle. 



. 94. PECULIARITIES IN THE OCCURRENCE OF COLORS. 



There exist several peculiarities in the occurrence of 

 colors among minerals, which, though from their want of 



