OXIDES 



as an iron ore. The hydrated ores of iron mined in the United 

 States a re ei.nl it often per cent . of the total product. They are mined 

 in Alabama, Virginia, Tennessee, Georgia, and Connecticut ; at 

 Salisbury in the latter state beautiful stalactitic specimens are 

 obtained. In the West it is used as a flux in the smelters. Large 

 quantities of limonite are used as a cheap metallic paint and as a 

 pigment in the coloring of mortars, as ocher, umber, and sienna; 

 alter the water is driven out by heat they form burnt umber or 

 burnt sienna. 



HYDRATED OXIDES OF ALUMINIUM 

 DIASPORE 



Diaspore. AIO(OH) ; A1 2 3 = 85.0, H 2 O = 15.0 ; Ortho- 

 rhombio ; Type, Didigonal Equatorial ; 4 : b : c = .9372 : 1 : .6038 ; 

 100 A 110 = 43 9'; 001 A 101 = 32 48'; 001 A Oil = 31 7' 

 35"; Common forms, c (001) ; b (010), m (110), h (210) ; Cleav- 

 age, brachypinacoidal eminent, h less so ; Brittle, fracture con- 

 choidal ; H. = 6.5-7 ; G. = 3.3-3.5 ; Color, white, yellowish, gray 

 to brown ; Streak, white ; Luster, brilliant to pearly on cleavage 

 faces; a = .702; \ = 1.750; a - -y = .048; Optically (+) ; Axial 

 plane = 010; Bx a = a. 



B.B. Most specimens decrepitate and yield water in the 

 closed tube ; after ignition with cobalt solution becomes blue. 

 Infusible ; after ignition, soluble in H 2 SO 4 , otherwise not attacked 

 by acids. 



General Description. When crystalline it is tabular or in 

 scales and flakes; also acicular with striations parallel to the c 

 axis. More often massive, encrusted or stalactitic. Generally 

 associated with corundum as in Macon County, North Carolina, 

 and especially with the impure form emery, as at Chester, Massa- 

 chusetts, and in Chester County, Pennsylvania. It is also found 

 with chloritic schists and in dolomites. As a decomposition 

 product it may be formed by the weathering of corundum, nephelite 

 and sodalite, or the reverse of this is also true, and diaspore by 

 dehydration forms corundum. 



GIBBSITE 



Gibbsite. Hydrargillite ; Hydroxide of aluminium, A1(OH) 3 ; 

 A1 2 O 3 = 65.4, H 2 O = 34.6 ; Monoclinic ; Type, Equatorial ; 



