42 COLORADO FERBERITE AND THE WOLFRAMITE SERIES. 



some of the rock specimens areas extending over many square centi- 

 meters are coated by minute crystals, few of which measure more than 

 a millimeter in any direction. Most of the crystals measured were 

 much smaller than the average. The dimensions of the crystals were 

 accurately measured under the microscope, so that their proportions 

 might be shown in the drawings for the text figures in this bulletin. 

 Of 18 crystals thus accurately measured the a axis lay between 0.3 and 

 0.7 millimeter on 14 crystals; the 6 axis (which in most of these crys- 

 tals has about half the true original value) between 0.5 and 2.5 milli- 

 meters on 16 crystals; and the c axis between 1.0 and 3. 5 millimeters 

 on 13 crystals. The extreme values are: a axis, 0.3 to 5.0 millimeters 

 (the 5.0 is an extreme value, the next highest is only 1.5; all the other 

 values are less than 1.0 millimeter); & axis, 0.6 to 3.2 millimeters; c 

 axis, 0.3 to 3.8 millimeters. 



Most of the crystals measured were bounded on one side by a cleav- 

 age face of &(010), so that the sizes here given do not actually repre- 

 sent the size of the original crystals in the direction of the & axis. In 

 the illustrations (figs. 3 to 34) the crystals are generally shown rela- 

 tively longer in the & axis than the measured values indicate, in order 

 to represent more truly their actual original sizes. The b axis on 

 many of the complete crystals was probably twice as great as 

 measured. 



COLOR AND CLEAVAGE. 



The crystals are black and their luster is splendent, nearly metallic. 

 The streak is dark brown, suggesting hematite. It is distinctly not 

 blak. Cleavage is clinopinacoidal, 6{010}, very good, and commonly 

 visible on the basal pinacoid. 



THE MEASURED CRYSTALS BY LOCALITIES. 



In the following table the crystals measured are grouped according 

 to the mine from which they came. In addition their general 

 character and habit are given for reference. These descriptions and 

 localities are based entirely on the material collected by Mr. Hess. 

 For other localities, not mentioned here, the papers given by Mr. Hess 

 hi his bibliography should be consulted. 



