450 S&. L. Penfield—Tiemannite and Metacinnabarite. 
A analysis was made by decomposing the mineral in a cur- 
rent of chlorine gas, precipitating the mercury as sub-chloride 
by means of phosphorous acid and the selenium with sulphar- 
ous anhydride. The results are given below with the deter- 
minations of small amounts of sulphur, cadmium and insoluble 
residue, : 
Ratio 
Se 29°19 _. 369), 
s 37 ost — eek 
Hg 69°84. 349 
Cd 34 0035 352 0-92 
Insol. 06 
99°80 
The ratio of the selenium plus sulphur to the metals is 1 : 0°93 
or nearly 1: 1, that required by a normal selenide, and as the 
impurities are present only in very small quantities the min- 
eral may be regarded as a simple selenide of mercury. e 
analysis agrees more closely with the theoretical requirements 
than any previously published, which may be in consequence 0 
the greater purity of the crystallized material. 
The crystals measure up to 8™™ in diameter. They are 
isometric, tetrahedral, and the habit of the few at my disposal 
is quite various. The plus and minus tetrahedrons are usually 
about equally developed and vary in luster; the cubic faces are 
also prominent and are at times ‘striated diagonally parallel to 
ally dull, o/(111, —1) lustrous, a(001, i-i), w(511, +5-5) and 
9733, +4-1). The above forms were all observed on one 
twin crystal, fig. 1, the latter y, as a very small face but giving 
distinct reflections. The faces in both halves of the twin cry 
tal figured are lettered alike except that those in twin positio® 
are underscored. Twins on the specimens in my possessio? 
are more common than single crystals, some of them show!nS 
simply both tetrahedrons and cube. 
