366 MINERALOGY 



a : b:c = 1.7089:1: 1.9184; P = 85 29' = 100 A 110; 001,101 

 = 50 50'; 001 A Oil = 62 24'; Common forms, c (001), a (100), 

 m (110) ; Cleavage, basal, micaceous laminae tough and wills how 

 percussion figures as in mica ; H. = 2.5-3.5 ; G. = 2.28-2.42 ; 

 Color, white, green, gray, or reddish ; Streak, white; a = 1.5347 

 y = 1.5577; -y-a = .023; Optically (+) ; Bx a in the angle p, 

 20 57' from c ; Axial plane = 010. 



B.B. Like diaspore, except it is soluble in H 2 SO 4 and in potassa 

 solution. 



General description. Hydrargillite, the crystalline form, is 

 rare; it occurs in tabular habit, parallel to the base and with a 

 hexagonal outline ; more often botryoidal, stalactitic, or in crusts, 

 as in Dutchess and Orange counties, New York, and at Richmond, 

 Massachusetts. 



Gibbsite is not a common mineral and occurs under the same con- 

 ditions and associations as diaspore. 



Artificial scaly crystals may be prepared by passing CO 2 through 

 a hot alkaline solution of aluminium hydroxide. 



BAUXITE 



Bauxite. A1 2 3 . 2H 2 O ; A1 2 3 = 73.9, H 2 = 26.1, but vari- 

 able ; Amorphous ; H. = 1-3 ; G. = 2.4-2.55 ; Color, white, gray, 

 when iron is present yellowish or red ; Streak, white ; Luster, dull 

 to earthy; Opaque. 



B.B Infusible, yields water in the closed tube, and is little 

 attacked by acids; otherwise like diaspore. 



General description. In large deposits it is claylike, or 

 oolitic and porous ; usually brown or red from iron. It was orig- 

 inally described from Baux, France, where it was found in dis- 

 seminated grains in a compact limestone. Its origin has been 

 attributed to the direct weathering of basalt-like rocks ; this seems 

 to be certainly so in some German localities ; from rhyolites ; 

 or again, as in case of the Arkansas bauxites, connected with the 

 decomposition of syenites. Other bauxites have been formed as a 

 chemical precipitate, when hot ascending waters have brought 

 solutions of alumina to the surface, where they have been precip- 

 itated by calcium or other carbonates. 



The bauxite deposits of the United States are found in Ala- 

 bama, Georgia, and Arkansas, where it is mined in large quantities. 



