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J. W. Mallet on a Zeolitic Mineral. 179 
Art. XIV.—On @ Zeolitic mineral (allied to Stilbite) from the Isle 
of Skye, Scotland; by J. W. Matter, Ph.D. 
THE specimen to which the following description refers has 
een in my ion for several years, and has attached to it a 
label bearing the name “ Hypostilbite,” but analysis shows it to 
be a mineral quite distinct from Beudant's hypostilbite of the 
Faroe Islands, and differing also from both stilbite proper and 
epistilbite. 
Tt occurs as a mass of minute crystals, resembling white loaf 
sugar, breaking easily, and crushing under the fingers into a 
coarsish crystalline powder. The Separate grains viewed under 
the microscope appear as single prismatic crystals or little groups 
of three or four, nearly transparent, colorless, and with a pearly 
lustre, especially on two opposite faces,—closely resembling stil- 
bite in fact in general appearance, 
The crystalline form could not be satisfactorily made out, but 
seemed to be monoclinic. Hardness a little greater than that of 
calcite. Specific gravity =2-252. ; 
trong muriatic acid poured over the pulverized mineral at 
night had the next morning formed a distinct jelly. 
On analysis the following results were obtain 
Atoms. 
RR es y.as bic.y daeest exis 63°95 = 1:191—3 
Ps eu crk ca ox: 40 0c: 20°18 "892—1 
ices re, cay. chaos 12°86 ‘459—L‘17 
ok oy 66.6 cesses wk ss ce 
Potash (with a little soda), .... ‘87 
OO 2s keine 00. ee ee 12°42. 1:380—3-52 
100°28 
Neglecting the small quantity of alkali, these numbers lead 
us nearly to the formula, 
- &(CaO, SiO s)+2(AlaOa, 28i03)+7H0, 
which differs completely from that of stilbite, CaO, SiO;+Als 
Os, 3SiOs + 6HO, or that of epistilbite, CaO, SiO. + AlzOs, 
83i0:+5HO. The percentage of water is also far too small for 
hypostilbite. sie 3 
The mineral appears to be a distinct one, and does not seem 
to have resulted from the gradual decomposition or change of 
any other; but it is perhaps scarcely desirable to add to the 
already numerous names of stilbite-like minerals by adopting a 
hew one for this substance until additional analyses of these 
nearly related species shall permit of their more accurate classi- 
