456 A, G. Dana—Gahnite of Rowe, Mass. 
The mineral was decomposed by repeated fusion with K,S,0.. 
The insoluble residue having been filtered off, the zine was 
thrown down as sulphide by H,S in an HC! solution—accord- 
ing to the method elaborated by Mr. Osborne of this labora- 
tory*—then dissolved and re-precipitated as carbonate. The 
ignited ZnO was examined for iron and the small amount 
found taken into account. The alumina and iron were twice 
precipitated as hydroxides with NH,OH and weighed together. 
The iron was determined by titration with permanganate 0 
potash, and the alumina obtained by difference. The amount 
of iron obtained was divided between the protoxide and sesqul- 
oxide in such proportion that the oxygen ratio should be as 
the formula demanded. The magnesium was weighed as pyro- 
phosphate. 
Besides the pyrite, which is seldom found in crystals of any 
size, the chalcopyrite and the quartz, the minerals associated 
more or less intimately with the gahnite are: thin plates of 
titanic iron, sometimes an inch across; steel gray rutile, occa- 
sionally in good erystals; apatite in small light green crystals ; 
sphalerite; garnet; calcite; a triclinic feldspar in greenish 
crystals, and epidote. 
he epidote occurs in curving, thick columnar forms and 
mostly in the pyrite. It is nearly opaque and of a greenish 
gray color passing into ash gray. tees 
An analysis showed that it had the following composition « 
II Mean 
i ati ous. REE ae to 38°18 38°23 38°20 
Al,O3 24°57 24°66 24°62 
Fe,03 12°16 12°24 12°20 
MnO (two separate portions)... ‘57 “57 = 
M : 7 : 
Cad 21°64 21°54 21°59 
Alkalies (one portion).....--. “87 37 37 
2 2°15 2°17 2°16 
Insoluble residue... ....--.. *35 34 
100711 100°26 100°19 
Ca: R: Si = 409: 935: 1:272 or nearly 4: 9: 12 
In this connection it may be interesting to add that nies 
recent visit to Franklin Furnace, New Jersey, I found the 
gahnite imbedded in magnetite from the “Trotter” mine. 
One crystal 8, of an inch in diameter had the planes 0, 1, 
t and 3-3 well developed. : 
Laboratory of the Sheffield Scientific School, April, 1885. 
* Am. Chem. Journ., vi, No. 3. 
