i died 5 aie 
acne, sabes tia 
{See 
. 56 ; J. Lawrence Smith on Emery. 
in order to show well all the plan 
than any yet known. Not wishing to lose so favorable an occa- 
sion to verify the crystallography of diaspore, I requested M. Du- 
frenoy to undertake the measurement of the angles, and it is to 
this able professor that we are indebted for the crystallographic 
results here given. 
la. 2 
The crystals are elohgated needles crossing each other in all 
directions like an acicular variety of arragonite from the Vosges. 
They resemble small crystals of topaz in lustre and in the dispo- 
sition of the vertical striz on the faces g. heir color is yellowish 
white. They are strongly dichroitic, the summits tinder certain 
inclinations appear black as if the light was completely polarized. 
The cleavage is very easy parallel to the face g', and it is this 
cleavage that gives a lamellar structure to that diaspore which is 
not in the form of needles. his cleavage notwithstanding its 
facility does not expose surfaces that reflect with great accuracy ; 
at first sight would not appear to exist, only becoming evident 
when the angle is examined. 
he crystals, very much flattened parallel to the face g', are 
represéhted by figures 2 and 3; the face g' does not exist, being 
replaced by three series of faces g’, the angles of which could not 
measured, but the almost absolute identity of these crystals 
with those of St. Gothard, which M. Marignac first described, 
* Three of the crystals measured are in the Cabinet of the School of Mines and 
Garden of Plants at Paris. = es : Z 
The second crystal above is nearly as thin as the first, although represented thicker _ 
ee PRR 
