THE PROPERTIES OF MINERALS. 663 



Examples. 



Crocoite— Berezov, Siberia. (Cat. No. 49581, U.S.N.M.) 

 Yauquelinite — Ben-zov, Siberia. (Cat. No. 45289, U.S.N.M.) 



Oxygen salts, molyhdates and tungstates. — The molybdates and tung- 

 state.s — conipouuds of oxides with oxides \yhose negative parts are 

 taken by molybdenum or tungsten trioxide — are few, there being, in 

 fact, about a~ dozen kinds only of minerals of this class. 



Examples. 



Wulfetiite — North Star mine, Lucien district, Elko County, Nevada. (Cat. No. 

 15981, U.S.N.M.) 

 Wolframite— Zinnwald, Saxony. (Cat. No. 8133, U.S.N.M.) 

 Hiibnerite— North Star mine, Silverton, Colorado. (Cat. No. 81150, U.S.N.M.) 

 Scheelite— near Santiago, Chile. (Cat. No. 6992, U.S.N.M.) 



O.rygen salts, uranates. — The uranates — compounds of the oxides of 

 uranium with other oxides — are very comi^lex in composition. They 

 contain, in addition to the oxides of uranium, the oxides of thorium, 

 zirconium, yttrium, and the cerium metals. Certain of the uranates 

 also contain nitrogen, argon, and helium in an unknown state of com- 

 bination. 



The type is represented by : 



Urauiuite — Wood mine, Central, Colorado. (Cat. No. 83759, U.S.N.M.) 



Compounds of organic origin. — This class includes the native salts of 

 organic acids such as the oxalates and mellates, the oxygenated 

 hydrocarbons, as the anibers and various fossil resins, together with 

 the numerous carbon comi)ounds like the petroleums, asphaltums, and 

 mineral coals, which are, in general, simply mixtures. 



Examples. 



Whewellite— Zwickau, Saxony. (Cat. No. 1920, U.S.N.M.) 

 Mellite— Russia. (Cat. No. 1219, U.S.N.M.) 

 Amber— Baltic Sea. (Cat. No. 15009, U.S.N.M.) 

 Petroleum— Pennsylvania. (Cat. No. 50409, U.S.N.M.) 

 Aspbaltum— Trinidad. (Cat. No. 50410, U.S.N.M.) 

 Uintahite— Uinta Valley, Utah. (Cat. No. 50411, U.S.N.M.) 

 Coal— Pennsylvania. (Cat. No, 50509, U.S.N.M.) 



VARIATIONS IN COMPOSITION. 



A mineral is primarily a body having a certain and definite chemi- 

 cal composition. This ideal condition is not always present, and the 

 composition of any one species may vary within wide limits. This 

 variation in composition may be due to: Original mixtures — that is, 

 \\hen tv<'o or more minerals are so intimately mixed that the mass 

 appears uniform ; metasoniatosis, in which a mineral originally 

 homogeneous may be partially altered by a process of "indefinite sub- 

 stitution and replacement;" chemical substitution, in which there has 

 been a complete or partial substitution of one or more elements for 



