44 NEW YORK STATE MUSEUM 



Color 



The color of a mineral is a matter of considerable variation, 

 different specimens of the same species frequently differing 

 through quite a wide range. This is notably so of the minerals 

 of nonmetallic luster, as in the case of fluorite, which is found 

 in white, yellow, green, rose-red, violet, blue, brown, wine color 

 and greenish blue varieties. Metallic minerals are far more con- 

 stant in color, a fresh fracture ordinarily giving the character- 

 istic color of the species. 



The color of the fine powder of a mineral is known as its 

 streak and often differs from the color of the hand specimen. 

 With soft minerals it may be readily obtained by rubbing the 

 specimen on a piece joi unglazed porcelain. 



General principles of chemical classification 



A substance which can not be decomposed or separated into 

 simpler constituents is known as an element. About 70 such 

 elements are recognized at present, less than half of which are of 

 common occurrence. It is estimated 1 that 99$ of the solid crust 

 of the earth for a depth of 10 miles is composed of eight elements 

 as follows: 



oxygen 47.3$ calcium 3.8$ 



silicon 27.2 magnesium 2.7 



aluminium 7.8 sodium 2.4 



iron 5.4 potassium 2.4 



For convenience elements are represented in chemical formulas 

 by symbols which consist of the initial letter of the name of 

 the element or an abbreviation composed of two letters, thus: 

 P=phosphorus Na^sodium (natrium) 



S=sulfur Ca;=calciuni 



0=oxygen • Pb=lead (plumbum) etc. 



In the appendix will be found a table giving the names of 

 the elements, their symbols and their relative atomic weight. 

 Some elements occur native or alone in nature, such as gold, 

 silver, copper, carbon, sulfur, etc. but the great majority of 



1 Clarke, F. W. Relative abundance of the chemical elements. Phil. soc. 

 of Washington. Bui. 9. 1889. p. 13S. 



