256 A. J. Moses — New Mercury Minerals from Texas. 



length. This material on examination is found to be quite 

 distinct from the eglestonite with which it is associated. In 

 one of the specimens the central portion was a mass of this 

 yellow substance and outside of this was a thick crust of 

 eglestonite crystals, while scattered through the crust were 

 globular masses of native mercury coated with the oxide mon- 

 troydite. 



Crystalline Forms of Terlinguaite. — Few crystals were satis- 

 factory for measurement. Four were measured whicli may be 

 briefly described as follows : 



Crystal 1. — Yery minute and complex, yielding reflections 

 from about twenty definite polygonal faces. Ko figure was 

 drawn because of the difficulty of judging relative develop- 

 ment of forms, a, c, ??z, ?/, A, g^ a, X were the most prominent 

 forms. 



Crystal 2. — Larger and simjDler than crystal 1, and elongated 

 parallel to the axis h. The principal forms are shown in fig 2 in 

 approximately the relative size. 



Crystal 3. — Short and relatively thick and complex crystal. 

 The principal forms are shown in fig. 3. 



Crystal %. — Tabular parallel a \ 100 ( . Showing prominently 

 also ^, 7 and it and less prominently S, fZ, ^, u^ x, ^, ^, ^, \. No 

 drawing was made of this crystal. 



The crystals were mounted with their most prominent zone 

 normal to the vertical circle. The axis of this zone proved to 

 be the only axis of symmetry and therefore was the axis of h 

 of the monoclinic system. By trial in the stereographic pro- 

 jection the forms denoted by c and a were found to be the 

 most prominent zone centers and were chosen as |001[ and 



jioos. 



The angles obtained by measuring with the axis b normal to 

 the vertical circle were transformed to the conventional (^ and 

 p angles referred to a pole plane at right angles to the c axis 

 and to a meridian through j010(. Tliese angles are here tabu- 

 lated and with tliem the calculated angles for the particular 

 indices and calculated axial elements. 



