Mineralogy and Petrography. 



methods 1 already noted in tins*- pairt 

 to be composed simply of mica niol 

 intermingled with molecules posses.-i 

 chlorite. • Many analyses of vermicu 

 of them bear evidence of careful w 

 phite 2 occurs in the Leadhills. South* 

 au irregular fracture. It melts easil; 

 and dissolves in hydrochloric acid, le 

 sity is 6.9-7.0, and in composition it 

 and phosphorus partly replaced by a 



l.o0 



Crystallographic— Barite crystals from veins cutting limonite and 

 siderite, forming lenticular masses in limestone, interstratificd with crys- 

 talline schists at Huttenberg, Saxony, have been studied by Biunlecb- 

 ner 3 . They are supposed to have originated by the leaching of barium 

 silicate and its decomposition through the agency of carbonic acid into 

 barium bicarbonate and silica, and by the further action of iron sul- 

 phate upon the barium salt. Well formed crystals are rare, but the 

 author has succeeded in detecting upon them twenty-nine forms, of 

 which the following are new: ocPV', oo P22, oo P30, x P44, x V-. 



16P^, 20P^ and 4P|. An examination of the crystals of uUnvm- 



ite from Sardinia, in the possession of the British Museum, inclines 

 Miers 4 to regard them as interpenetration twins of tetartohedral form.-. 

 whose apparent holohedral symmetry is due to twinning about the 

 dodecahedral axis. If this is so, ullmanite is the first regular tetarto- 

 hedral mineral known. Melville 5 has investigated the dial 



tals in the cavities of the quartz diaspore rock of Mt. Robinson*. One 

 type consists of light-brown transparent forms, elongated parallel to c. 

 Its planes in the order of their development are oc P^, oo P, oo P2, 

 oo Pf, oo P|, P^T, P and P2, with the axial ratio = .6457 : 1 : 1.0689. 

 A second type comprises almost white, opaque crystals with a stout 



pyramidal habit, bounded by oo P2, Pj and oo P^. A very elabor- 



^merican Naturalist, 1891, p. 830. 

 a ColHe: Jour. Chem. Soc, lv, 1889, p. 91. 

 3 Min. u. Petrog. Mitth. xii, p. 62. 

 4 Min. Magazine, ix, p. 211. 

 5 Am. Jour. Sci., June, 1891, p. 470. 

 ' «Cf. American Naturalist, 1892, p. 166. 



