GEOLOGY AND MINERALOGY. 527: 
over amorphous sesqui-oxide of iron in a heated porcelain tube, crystals of 
specular iron ore resembling in part those of Elba, and partly the flattened vol- 
canic forms, were readily obtained. If the current be sufficiently slow, not a 
trace of a chloride is produced in this experiment, and the acid consequently is 
in no way decomposed. The crystals thus formed by M. Deville were capable 
of being measured. The intervention of aqueous vapour was found to be quite 
unnecessary, the gas acting perfectly in an absolutely dry condition. Prot- 
oxide of iron, as obtained by the process of Debray, yielded under this treat- 
. ment a number of small octahedrons possessing the exact composition of magnetic 
tron ore. A mixture of sesqui-oxide of iron and calcined magnesia gave, in 
like manner, octahedrons with truncated edges, having the theoretical compo- | 
sition of pure maguo-ferri/e. Calcined magnesia alone, under a slow current 
of hydrochloric acid, yielded small octahedral crystals of periclase, without the 
slightest loss or change accruing to the acid itself. AMuwsmannite was also 
formed in dimetric octahedrons (of 104° to 105° over polar edges) from red 
oxide of manganese. Cassiterile, by the same process, in crystals of great 
beauty, from amorphous oxide of tin. The crystals were dimetric octahedrons 
with their basal edges and angles replaced by the two square prisms, these 
shewing the proper interfacial inclinations of 135°. Finally, amorphous titanic 
acid furnished minute crystals of a blue colour and great brilliancy, belonging 
either to Rutile or Anatase, most probably to the former. Deville’s experiments 
are given in detail in several numbers of the Comptes Rendus of June and July 
of the present year. They shed quite a new light on the formation of many 
erystallized substances in volcanic and other localities, and take rank amongst 
the most important contributions of the day to chemical geology. 
Brucite:—The Brucite of Wood’s Mine, Texas, has been described by Hermann, 
(Jour, fur Prakt. Chem. \xxxii., p. 368), under the name of Zé.ralite as a mono- 
clinic modification of the hydrate of magnesia. This view, however, has been 
subsequently shewn to be erroneous by Professor George J. Brush of Yale 
College. Prof. Brush (Amermwan Journal of Science and Aris, July, 1861), 
proves clearly the identity of the so-called Vexalite with Brucite, and shews 
that both are hexagonal. 
Staurolite :—The composition of Staurolite, as determined more especially by 
the careful analyses of Jacosson, is well known to vary greatly with regard to 
the respective amounts of silica and alumina. Rammelsberg has recently under- 
taken a further examination of this mineral (Ber. d. Adng/. preuss, Akud. d. 
Wiss. zu Berlin, Mdrz, 1861), but with the same general results, so far at least 
ag respects its atomic constitution. Analyses of ten examples from various 
localities shew such different results—the silica varying, for example, from 28°86 
to 51°32—that no one common formula can be adopted for all. But Rammels- 
berg shews, in addition to this, that the iron in the mineral is chiefly present in 
the state of protoride, whilst all previous analyses had given it as sesqui-oxide. 
The writer of these notes, however, so long ago as 1848, ina short paper pub- 
lished in the Chemical Gazette of July 15 of that year, (‘On the Composition of 
Acmite,” &c., by E. J. Chapman), called attention to the fact that by the em- 
Vor.- VI. 20 
