Geology and Mineralogy. 359 



feldspars which undoubtedly contain barbierite in isonaorphous 

 admixture. See also, for example, the orthoclase described by 

 Ford.* 



Chemical Laboratory, U. S. Geological Survey. 



10. Brief notices of some recently described Minerals (see p. 

 90, vol. xxx). — WiLTSHiREiTK is a new species from that most 

 prolific locality, the Binnenthal in Switzerland ; it is described 

 by W. J. Lewis. It occurs in small crystals grouped in parallel 

 position and associated with sartorite in a cavity in the well- 

 known dolomite of the region. The color is tin-white with occa- 

 sionally a russet tarnish. The material thus far available is too 

 scanty for a determination of the chemical composition, but it is 

 regarded as probably a sulpharsenite of lead. The crystals are 

 monoclinic and are referred to the axes: a : b : c= 1'581 : I : 

 1-070 ; (8 =: 79" 16. The habit is prismatic, the crystals being 

 elongated in the vertical direction, in which zone the faces are 

 strongly striated. The hemidomes are, however, smooth and 

 bright and the same is true of the hemipyramids. The mineral 

 is named in honor of the late Rev. Thomas Wiltshire, at one 

 time Professor of Mineralogy in Kings College, London. — I^hil. 

 May., September, 1910, p. 474, 



MiNGUETiTE is a hydrated iron silicate described by A. Lacroix 

 and regarded by him as intermediate between stilpnomelane and 

 lepidomelane ; it had been called biotite. It forms masses of a 

 greenish black color consisting of confused aggregates of small 

 brittle plates ; these are opaque except when very thin and in 

 that case they sIioav a dislocated black cross of negative character. 

 The specific gravity is 2 '86 and the composition is given by the 

 analysis (by Pisani) : 



SiOs AloOa Fe,03 FeO MgO CaO Na^O K^O H^O 

 43-65 5-22 18-80 1900 3-32 0-94 0-66 300 6-00 = 100-49 



From the above the formula calculated is 17SiO„ . 4Fej03 . 

 8FeO . K^O . 8H.^0. A small part of the ferric iron is replaced 

 by aluminium. The name given refers to the mine, Minguet, at 

 which it was found ; this is situated in the Segre region, Maine 

 et Loire, France. — Bull. 8oc. Frang,. Min., xxxiii, 270. 



Stellerite is a zeolitic mineral allied to heuiandite and stil- 

 bite, described by J. Morozewicz from a diabase tuff on one of 

 the Commander islands in Bering Sea. It occui-s in crystals 

 which are orthorhombic both in lorra and optically ; these are 

 tabular in habit, resembling stilbite, and show perfect cleavage 

 parallel to b. Hardness 3-5-4, specific gravity 2-1 2. Analysis 

 gave : 



SiO.2 



AI2O3 



Fe203 



CaO 



NajO 



H.O 



59-33 



14-41 



0-33 



8-33 



tr. 



18-15 



100-34 



From this the formula obtained is CaAljSi^O,^ . 7HjO ; this is 



* On Orthoclase Twins of Unusual Habit, this Journal, xxvi, p. 149, 

 1908. 



