: Mineralogy and Geology. 269 
The eryolite on which the crystals were found is not of good quality, 
that is to say, it is much mixed with other minerals. - purer cryolite 
cargoes have never afforded me any traces of crystals. They occurred 
over the exterior of the large masses, and only in one © instance have I 
found them lining a cavity. They were covered in all cases with a red 
mineral, 
t common form is a rectangular prism, either short and tabu- 
= or long; the former sometimes 6 mm. square; the latter small, not 
exceeding 3mm. in length. The prisms have os? a replacement 
of two of the angles by a triangular plane (a); and the base and sides 
are og Nah striated in a direction parallel to the sides of this plane, 
and i me direction when the plane is absent. The prisms are 
grouped one over another, giving a stair-like surface, which is mostly 
covered by the red mineral ‘diudea to. Where this mineral is absent, or 
va are respectively 126° 50’ san 109° 16’, Planes 
of 0} siesta oi pyramids exist, but they are all very small. How- 
ever incomplete this wong there can be no doubt that the crystals 
are trimetric in char 
y Pisani na other chemists and howe to be clin , ne 
the true seach oes “ a8 of wn aa B.C, of whieh he had only 
0'146 of a gram for mica] exam 
But Prof. Shepard xs -pebtialved in + this deel and elsewhere that 
‘Am. Jour. Sc1.—Srconp Series, Vou. XLII, No. 125.—Serr., 1866. 
30 
