Adtilaria and Other Secondary Minerals. — Wi?ichell. 3 1 7 
[Contributious to the Mineralogy of Minnesota. VII.] 
ADULARIA AND OTHER SECONDARY MINERALS 
OF THE COPPER-BEARING ROCKS. 
By N. H. WiNCHELL, Minneapolis, Minn. 
AdiUaria. Prof. J. D. Whitney gave an analysis of a miner- 
al found* by him at Copper Falls and at Douglass Houghton 
mine, Keweenaw point, where il: occurs implanted on quartz 
and copper, and which gave the following analysis: 
Silica 65.88 
Alumina 17-35 
Oxide of Iron 57 
Potash and soda (by loss) 16.20 
100.00 
He made nO' direct determination of the alkalies, not having 
been able to obtain enough of the substance for such analysis. 
A similar mineral was found by the writer at the Minong 
mine on Isle Royale, where it forms a thick coating on metallic 
copper, and is associated with calcite. It also forms geodic 
coatings and in these cavities (though small and irregular) can 
be seen and studied the crystalline form and faces. The min- 
eral is insoluble and infusible, or difficultly fusible. In a tube 
it gives no water. By the Boricky and the Behrens tests for 
potash, many characteristic crystals were obtained. By the 
former me'thod some lime and some soda were also indicated, 
but plainly in subordinate amounts. The crystals are small 
(from I. to 1.5 mm in transverse diameter) and have a glassy 
transparency between crossed nicols. The fracture is irregu- 
larly conchoidal, but governed partially by the cleavage. 
Broken at random the fragments give more numerous cleav- 
ages in which the axis//m is vertical than those having n^ ver- 
tical. The crystals are confusedly mingled and apparently 
compounded by parallel but slightly irregular growths, which 
cause an extinction which is not simultaneous, but takes place 
on one side sooner than on another. The acute optic angle is 
small and contains //p the appearance being almost that of a 
uniaxial mineral unless the linage be well centred. 
The crystals are mono-clinic and the prismatic faces are the 
only faces of the perpendicular zone, the optic plane being par- 
allel to the diagonal of a cross-section. Refraction and double 
♦Report on the Lake Superior land district. Part II, p. 102, 1851. 
