OXIDES 



holes. The decomposed dyke furnished much easier digging for 

 these little animals th:m tin- hard crystalline limestone adjacent. 

 ( 'orumlum is also found all along the Blue Ridge in Virginia, North 

 ami South ( 'arolinus, and (leorgia. Very fine blue specimens have 

 1 iei-1 1 obtained at Sparta, New Jersey, and at various points in 

 Sussex County. Most of the " adamantine spar " used in the 

 I'nited States is mined in Renfrew County, Ontario, where it occurs 

 in a coarse pink syenite. Emery is a compact or granular variety of 

 corundum which is mixed with a large proportion of oxides of iron. 

 It is mined at Chester, Massachusetts, and at Peekskill, New York. 

 In the latter locality it is associated with hercynite, magnetite, and 

 garnet, and occurs as a segregation product from the norite of the 

 Courtland series. Abroad emery is mined in Asia Minor, Tur- 

 key, and Greece ; 60 per cent, of this product is exported to the 

 United States. 



Corundum and emery are commercially used as an abrasive, espe- 

 cially in emery paper for polishing and cleaning metals ; in wheels 

 for sharpening steel tools, and in the cutting of glassware, though 

 artificial corundum made from bauxite by heating it to a high tem- 

 perature in an electric furnace is fast replacing the natural mineral. 



Artificial crystallized A1 2 O 3 may be produced by fusing equal 

 parts of Al 2 0s and lead oxide, and allowing the fusion to cool 

 slowly, when tabular crystals of corundum separate; if a little 

 oxide of cobalt is added, they will be sapphire-blue ; if a little po- 

 tassium dichromate is added they will be ruby-red. The so-called 

 reconstructed rubies are formed in the oxyhydrogen flame; by 

 rotating a small crystal rapidly in the flame with the temperature 

 near the fusing point, it is then built up with fine particles of natural 

 ruby, the color being regulated by the amount of chromium 

 present. These artificial stones in their physical properties differ 

 in no way from the natural ruby, and they puzzle even the expert 

 to recognize them. They have however peculiar circular markings 

 or pores, due to the rotation in the flame while in a semifused con- 

 dition, which are a material aid in their identification. 



HEMATITE 



Hematite. Red oxide of iron, Fe 2 O 3 ; Fe = 70, O = 30 ; 

 Hexagonal; Type, Dihexagonal Alternating; 6 = 1.3656; 0001 A 

 1011 = 57 37'j r^ = 94; Common forms, c(0001), r(1011), 

 e (OlTl), u (10H) ; n (2243) ; m (10TO) ; Twinning plane r, both 



