A. J. Moses — Mineralogical Notes. 



489 



The accompanying figure (2) copies striations observed upon 

 two crystals ; the upper left hand octahedral face in particular 

 is a fairly accurate reproduction. The striations on octahedral 

 faces rarely if ever cross and in each face are parallel always 



either to its intersections with the cube or with the pyritohe- 

 dron i-1. The striations on the diploid and the pyritohedron 

 were not parallel to intersections with the cube but to inter- 

 sections with each other (or with the octahedron). No stria- 

 tions were observed on any cube face. 



2. Ettringite from Tombstone, Arizona, and a formula for 



Ettringite. 



The first specimen of this mineral I received over a year ago 

 and proved it to be a hydrated sulphate of alumina and lime, 

 but was prevented from making a complete examination by the 

 small amount of material available. Since that time I have 

 received and examined several other specimens. 



The mineral was found by Mr. W. F. Staunton in an ore 

 shoot in the white crystalline limestone of the Lucky-Cuss 

 Mine, Tombstone, Arizona ; just at the water level. It occurs 

 incrusting a massive silicate of lime and alumina from which 

 it has apparently been produced by the action of sulphuric 

 acid, as it frequently fills little veins and hollows in the silicate 

 and the latter is usually in these portions loosely coherent as if 

 corroded. 



In appearance the sulphate resembles a fibrous pectolite as 

 it is made up of white somewhat translucent radiating libers 

 of a length up to one inch, or sometimes in little bunches of 

 silky parallel fibers. 'No crystals have been found but the 

 fibers are doubly refracting and appear to extinguish parallel to 

 their length; cross fractures (or cleavage) approximately at right 

 angles to the length are frequent. The hardness is a little 

 over 2 and the specific gravity determined on 200 rag was T55.* 



* If the silicate in the sample is assumed to be of the specific gravity of the sili- 

 cate gangue (2 66) the gravity of the sulphate is reduced to 1*27, but the silicate 

 near the sulphate is very much altered and probably nearer the gravity of the 

 sulphate. 



