260 A. J. Moses — N'ew Mercury Minerals from Texas. 



gray in color, and although possessing very much the solidit}^ 

 of a soft amalgam and spoken of by Mr. Hill as a mixture of 

 cinnabar and mercury, was nevertheless entirely volatile and so 

 far as qualitative tests went was simply metallic mercury. 



In addition to the minute needles forming the velvety crusts 

 there were numerous larger transparent needles of darker red 

 color and of a length often exceeding one mm. These were 

 in most instances poorly terminated, striated and composite, but 

 occasional crystals showed terminations and the best of these 

 crystals was carefully measured in the two-circle goniometer. 

 Crystalline Form of Montroydite. — A very perfect doubly 

 terminated and highly modified crystal exceeding slightly one 

 mm. in length by one-third mm. in breadth, and suggesting 

 under the hand glass a general resemblance 

 ^ in habit to some crystals of topaz, was 



mounted with its longest direction normal 

 to the vertical circle and the orthorhom- 

 bic symmetry being soon made evident, this 

 direction was retained as that of the ver- 

 tical axis. The most prominent pyramidal 

 form a?, fig. 4, being very acute, the pyra- 

 mid in the same vertical zone was chosen 

 as the unit form. The more prominent 

 forms shown in lig. 4 are a JlOOf; h iOlOj; 

 m jllOf; rZjlOlJ \x\ZZ\\', o\\\\\\s\\Vi\\ 

 r)21l;- and ^jl32(. In addition to these, 

 faint reflections were obtained from faces 

 of microscopic dimensions corresponding to 

 '2^;3115 and ^|122;. 



The faces s are less prominent in the real 

 crystal than in the drawing from the presence 

 of indeterminate truncating faces. 

 In the calculation of the elements c and a most of the occur- 

 ring forms were considered and in proportion to the sharpness 

 of the signals yielded by their faces. The results were as 

 follows : 



Form. 



Factor. 



Value of a. 



Value of 



m 



u 



•63625 









2 



•63707 



1-1918 



X 



8 



•63748 



1-1894 



w 



2 



•64406 



1-1960 



t 



1 



•63729 



1-1985 



r 



2 



•63956 



1^2037 



e 



3 



•63670 



11941 



Averaore 



d = -63797 



c — 1-1931 



The form s jll2 • was not used in this calculation because 



