94 GJ. Brush on Crystalline Form of Hydrate of Magnesia. 
Art. XIV.—On the Crystalline Form of the Hydrate of Mogi 
Jrom Texas in Pennsylvania; by GEorGE J. Brus 
THE crystalline form of Brucite (MgH) was first studied by 
Prof. Dana, and shown by him to be rhombohedral,* the speci- 
mens examined were minute peewee See by the writer in 
the year 1852 at Low’s Mine in the town of Texas, Pennsylva- 
nia, Since then meee Boise he been found in grea 
abundance at Wood’s Mine exas; the crystals vary from a 
microscopic size to nee ia two or three inches in diameter, 
and crystalline plates with rough prismatic faces of a much larger 
size are of frequent occurrence. e crystals are generally thin 
hexagonal plates with rhombohedral planes almost obliterating 
the prism ; occasionally, however, the prism is oblong, the length 
being two or three times the breadt th; they are symmetrically 
modified hexagonal prisms, and cannot be retoived to any but 
the rhombohedral system. 
In a recent article in the Journal fiir praktische Chemie, 1xxxii, 
, R. Hermann describes the Texas mineral under the new 
cont 
ing a nou ce of manganese. The o tical ona 
rism, and is an apeeaibality in the monoclinic ero 
Besides the basal and the four lateral planes here referred to, 
the crystal described by Hermann contained two other planes 
on the acute angles of the pacar ase Dene caine with the 
and 157°. The sp ecimen examin ong by Her was most 
probably one of bess disto a crystals so sap met with 
in micaceous minerals. In some hundred or more specimens 
from this locality which I hia examined, the crystals are dis- 
* This Journal, [2], xvii, 83. 
