Geology and Mineralogy. 351 
Or 
4; specific gravity 4°15. In form it is closely related to fiinkite, 
but its chemical composition is not entirely settled, the following 
partial analysis by Mauzelius having been made on a very minute 
quantity (0°08 gr.): 
As,.0; MnO FeO PbO CaO MgO SiO. 4H,0O x 
24°4 30°2 ea O27", “0-2 277 0°5 8°4 146. =10%:9 
X including insoluble 4°3 and not identified 10:3. 
Another point of interest is the description of Ursanire (see 
this Journal, July, p. 76), which is shown to belong to the 
pyroxene group. An analysis by Mauzelius gave : 
SiO. Al,0; Fe,.0; FeO MnO CaO MgO Na.O K,0O ign, 
G.=3°32 51°61 O74 27°24 0°54 1°73 4:90 2°75 10°59 0°36 0:90 
. =T01- SG 
Descriptions are also given of a soda-richterite, a soda-berzeli- 
ite, of the partially known mineral caryinite, of crystallized 
safflorite, of magnetite in cubic crystals, ete. 
12. Ueber gewundene Bergkrystalle; von G. TscuERMAK, 
Vienna, 1894 (Denkschriften der K. Akad. Wissenschaften, vol. 
lxi).—The remarkable crystals of quartz, not uncommon in Switz- 
erland but known also from other localities, having curved faces 
and more cr less twisted axial systems, have been minutely studied 
by Tschermak. He, while confirming the early observations of 
Weiss as to the regularity of these growths, has gone further 
and offered an explanation for them. This is based on the assump- 
tion of the simultaneous existence of three different methods of 
twinning. ‘The first, which the majority of the specimens show, 
is the common law characteristic of many quartz crystals in which 
a plane of the hexagonal prism is the twinning plane. In the 
second law, the twinning plane is inclined to the vertical axis in 
the direction of the fundamental rhombohedron and very nearly 
perpendicular to it; in the third, the twinning plane is a face of a 
twelve-sided prism varying but little in position (only 1’ 40”) from 
that of the second prism. Several types of forms are shown to 
exist which are explained according as to whether two or three 
of these methods of twinnings coexist, and also determined by 
the method of their combination. The second and third twinning 
planes mentioned are properly vicinal planes, and hence the cor- 
responding twins may be called vicinal twins. At the same time 
the suggestion is made that these vicinal twinning planes become 
fundamental planes with simple indices if it is assumed that the 
erystallization of quartz is not hexagonal-trapezohedral (tetar- 
tohedral), but triclinic-hemihedral. The plates accompanying the 
text give beautiful representations of some of the remarkable 
forms described, in which not only the deep smoky-brown color, 
but even the luster of the surface are faithfully reproduced. 
