S. L. Penfield —Tiemannite and Metacinnabarite. 458 
The measured angles are as follows: 
87 
211 ~ 112 36° 54’ 
3 
Although the crystals are poorly adapted for measurement 
their habit is characteristically isometric tetrahedral, and the 
f 
After seeing the specimens at my disposal it seems strange that 
the name “ amorphous sulphide of mercury ” should have been 
80 long attached to this mineral. 
After carefully cleaning the crystals used for measurement 
and freeing them as far as possible from attached cinnabar, the 
Specific gravity was taken with great care on a chemical bal- 
ance, with 7°81 as the result. As the three crystals weighed 
Seether only -1684 grams the result can not be regarded as 
very accurate, but I thought it would serve to compare with 
the specific gravity of the amorphous sulphide given by Mr. 
oore as from 7°701—7'748 
The crystallographic results taken in connection with those 
On tiemannite, with which the mineral stands in close chemical 
relation, leaves little doubt as to the isomorphism of the two 
minerals, and the isometric character of metacinnabarite, while 
the intermediate chemical compounds to which the name 
onofrite has been applied and which are not known in crystals 
stand intermediate between the two in physical relations. 
' Relation between the selenides and sulphides of mercury.—As 
the deiinity which I found for the crystals of tiemannite, viz: 
‘19, was greater than that given by other authors (this usually 
being 71-74, Blum giving 7:8-7°88), I thought it would be 
best to take the density of the material from Clausthal, which 
was all that was at my disposal. The material was quite im- 
driven off, the density of the residue taken and th the 
pure material calculated. I also took the density vk three 
Specimens of onofrite from Utah; in these cases, however, the 
residue was smaller and was regarded as having a seanity of 
27. Undoubtedly it was heavier 28 igs true density of the 
mineral would be correspondingly lo 
All the densities er have been found are the dain’ 
I. Tiemannite, crystal 
i. Tiemannite, Cla natal after deducting 16 per cent of impurities 3 a7 
IIL. Tiemannite, Clausthal, after nai pie 39 per cent of impurities 8°305 
IV. Onofrite, Utah, after deducting 1°3 per cent of impurities ..--. 7-98 
« Onofrite. , Utah, — deducting 1-6 per cent of im purities ....- 8-09 
VI. Onofrite, Utah, after deducting 2°9 per cent of En: ak aa 8-04 
Metacinna nie California, IE is 5 a knees een a 
VIII. Metacinnabarite, California, amorphous, determined by Moore. . 4 1-15 
