Properties of some Minerals and their varieties. 268 
Besides the Danaite, we have added, for the sake of compari- 
son, the chemical composition of léllingite. Taking into con- 
sideration the fact that, in the compounds, arsenic and cobalt 
play the part of negative elements, but iron and also most of the 
sulphids that of positive, a partial explanation of the change of 
+ becomes possible. In the crystals from Franconia the per- 
centage of FeS is larger (=50°7) than that of AsCo (=48'1). 
The reverse is true in the danaite from Norway, where FeS 
=43°6 and CoAs=55°8. These varieties show a very marked 
difference in specific gravity. 
C. Skutterudite. 
Modum. Tunaberg. Skutterud. Kongsberg. 
= _ + 
G= 6934 6664 
As 79°0 
Co 19°5 
Fe 14 
Wohler* 
= 
Kongsberg could not be determined, as in the specimens at 
hand the mineral was in small imbedded portions. The varia- 
tion in the case of the varieties from Modum and Skutterud is 
especially remarkable. Complete crystals from the Skutterud 
locality were investigated, as well as massive specimens: they 
were all ++. Skutterudite is isometric, but no hemihedrism has 
been observed. 
D. Glaucodot. 
Hakansbé. Chili. 
Shell. Kernel. 
_ Total. ~ ? 
G= 6-011 5-905 
As (Fused B.B.to| 440 (|(FusedB.B.to| 43°2 
8 a pearl). 19°8 a pearl). 20°2 
Co 161 24°7 
Fe 19°3 110 
es 5973 5-975—6°003 
Ludwig.+ attner.t 
basal and prismatic, and may be observed not only in the 
outer layer of the crystal, but also in the central, although less 
perfectly. About twenty large crystals from Hakansb6 were 
vol. xliii, 591. 
Heenan Sitzungsberichte der k. Akad, Vienna, I, vol. ly, 445, 1867. 
Plattner, Pogg. Ann., vol. Lxvii, 127, 1849. 
