GUIDE TO THE MINERALOGIC COLLECTIONS 



71 



Oriental topaz. Yellow- 

 Oriental emerald. Green 

 Oriental amethyst. Purple 



An opaque variety of corundum occurs in coarse nodular 

 crystals with a marked rhombohedral parting and of a dull 

 blue, gray, brown or black color. 



The variety known as emery is granular in texture, of great 

 t ugliness and black or grayish black in color. It is commonly 

 intermingled with hematite or magnetite. This variety, which 

 is of great value as an abrasive, is found in a number of grades, 

 classed on the relative coarseness of the corundum crystals or 

 grains. 



The gem varieties of corundum are found in the gravel of 

 river beds in Upper Burma and Ceylon; some handsome gems 

 have been obtained from Montana and North Carolina. 



Corundum occurs in many crystalline rocks associated with 

 minerals of the chlorite group, tourmalin, spinel, cyanite, etc. 

 and has been observed in some of the younger volcanic rocks. 

 It is mined for emery in the island of Naxos, in Asia Minor, and 

 in the United States at Chester Mass., in Westchester county, 

 X. Y. and elsewhere. 



Hematite (specular iron) Fe 2 3 



Hematite is the sesquioxid of iron and contains 30^ oxygen and 

 70$ iron. 



Hematite crystallizes in the rhombohedral group of the 

 hexagonal system. The crystals are commonly thick or tabular 

 in habit (fig. 188) as distinct from the 

 tapering forms of corundum, and are 

 often reduced to thin plates w T hich in 

 some varieties group themselves in 

 rosettes (eisenrosen pi. 21J. Massive 

 forms in compact columnar, radiated and 

 kidney-shaped masses pass into loose 

 earthy varieties, containing more or less 

 clay. The luster of hematite varies with Hematite 

 its form from a splendent metallic, in the crystallized varieties, 

 to dull in the ocherous and argillaceous hematite; the color also 

 varies from iron-black to red. The streak is red in all varieties. 



