TO SE acta eS ep a CE ——— 
A. G. Dana—Gahnite of Rowe, Mass. 455 
Art. LVIII.—On the Gahnite of Rowe, Massachusetts; by 
ARNOLD Guyot DANA. 
IN some ecar-loads of pyrite brought to New Haven, Con- 
necticut, from the mines of J. M. Davis & Co., in the town 
of Rowe, Massachusetts, eight miles east of the Hoosac tunnel, 
I found some fragments of the mineral gahnite. On visit- 
ing the locality I learned that the gahnite occurred on the 
Outer portions of a “vein” or “Jenticular mass” of pyrite, of 
exceptional purity, varying from seven to twenty feet in thick- 
ness including rock is gneiss and schist. The mine had, 
at the time of my first visit, reached a depth of 200 feet. The 
waste heaps afforded a large amount of material and some good 
Specimens, though the hardness of the enclosing rock made it 
difficult to obtain the crystals unbroken. Part of them were 
entirely embedded in the pyrite and part seemed to have once 
ined cavities, most of which had since been filled in by quartz 
and the rest by chalcopyrite. 
_ The crystals in the quartz were greenish in color and some- 
umes had a slightly greasy lustre, while those in the pyrite 
were almost black, but green by transmitted light, and had a 
high vitreous lustre. These latter, though apparently the most 
pure, were so filled with minute particles of pyrite that for 
analysis it was necessary for the most part to use those in the 
uartz. 
_ The largest crystals had a diameter of three-quarters of an 
Inch, but the majority were much smaller. Their habit was 
octahedral, with the faces usually built up terrace-like from the 
alternations of the octahedron with the dodecahedron. Simple 
odecahedrons were rare. o other planes were observed, 
though many crystals were examined. Good examples of the 
Spinel twin were occasionally met with. 
The specific gravity taken on a piece of exceptional purity 
Weighing nearly two grams was 453. 
An analysis of the gahnite, made because of the refractory 
nature of the substance on half a gram, gave: 
I. Mean. 
Al.,O; LL Bee] 55°04 54°83 
WG a, 3:22 2°79 3-00 
eO * 3°25 3°49 $37 
MnO tr tr. 
MgO 1 1°86 1 
ZnO 36°91 36°93 36'92 
SiO, and insoluble residue--.. “48 
