1874.1] Mineralogy. 265 
other valuable forms of alumina, may be yielded by the further working of 
these deposits. We understand that some of the crystals have been examined 
microscopically by Mr. H. C. Sorby. 
For several years past Dr. F. A. Genth has devoted much attention to the 
study of Corundum, especially noting the characters of the associated minerals 
and the changes which corundum is supposed to undergo. ‘The results of his 
studies have been published in theshape of the first part of the ‘* Contributions 
from the Laboratory of the University of Pennsylvania.’? Although corundum 
has been found in America both in the Laurentian system and in rocks 
referred to the Taconic system, yet the greater part of the American corundum 
occurs in what is termed the chromiferous serpentine or chrysolite formation, 
and in the adjacent rocks. By comparing the associated minerals and the 
general conditions of occurrence of the emery and corundum of Asia Minor 
and the Grecian Archipelago with those of the most important American 
deposits, Dr. Genth is led to suggest a correspondence of geological age in 
the two cases. The author gives a long catalogue of minerals supposed to be 
produced by the alteration of corundum, and refers in some instances to true 
pseudomorphs as evidence of suchchanges, There are probably few geologists, 
however, who will be prepared to receive Dr. Genth’s theory which seeks to 
explain the origin of certain beds of mica-schist, chlorite-schist, and paragonite- 
slate, by the alteration of larger deposits of corundum. Among the minerals 
associated with the American corundum are four described as new species, or 
varieties, under the names of Dudleyite, Kerrite, Maconite, and Willcoxite. 
Dr. Fischer, well known for his microscopic studies of various minerals, has 
examined a number of specimens of so-called Cat’s-eye ; that is to say, quartz 
which presents, when polished, a curious band of light generally referred to 
the presence of enclosed fibres of asbestos. In all the specimens examined 
by Fischer he could find no trace of any fibres of asbestos, so that we are 
compelled to seek a new explanation of the fibrous character of the cat’s-eye. 
The quartz may either possess a true fibrous structure of its own, or it may 
have replaced some mineral which originally possessed such a structure. It 
is the latter conclusion that Dr. Fischer is disposed to accept. This conclusion 
is interesting in connection with Wibel’s examination of the cat’s-eye of the 
Cape, noticed in last quarter’s chronicles. Fischer’s paper will be found in 
Tschermak’s ‘‘ Mineralogische Mittheilungen,” published in Vienna. 
A new mineral-species belonging to the group of felspars has been lately 
described by Von Kobell, in the ‘* Journal fur Praktische Chemie,” under the 
name of Tschermakite,a name proposed in honour of Dr. Tschermak, who 
has done so much to simplify our views of this important group of rock- 
forming minerals. Tschermakite occurs at Bamle, in Norway, where it is 
associated with Kjerulfine. The new species is found in compact masses, 
with very perfe& cleavage in two directions, making an angle of 94°. These 
cleavage-planes show fine strie, similar to those on other triclinic felspars, 
Analysis gives—Silica, 66°57; alumina, 15°80; magnesia, 8-00; soda, with 
trace of potash, 6°80; water, 2°70=99'87. From this analysis may be deduced 
the formula -3(RO.3SiO2)+A1,03.3Si02. Tschermakite may therefore be 
regarded as a peculiar species of felspar, related to oligoclase, but containing no 
lime. 
An excellent monograph of the minerals grouped together under the 
general name of Brochantite, has been laid before the Vienna Academy. by Dr. 
Schrauf, and published in its ‘“‘Sitzungsberichte.”” He describes in much 
detail, and illustrates by admirable figures, the several forms of this mineral, 
of which four distinét types are recognised. It appears that Brochantite is not 
prismatic in crystallisation, but that most varieties are either monoclinic or 
triclinic. 
' The peculiar form of silica which Prof. Maskelyne some time ago discovered 
in the Breitenbach meteorite, and described under the name of Asmanite, has 
been recently studied by Prof. Vom Rath. His conclusions confirm those of 
Maskelyne, respecting the specific gravity, degree of hardness, and chemical 
