364 Brush and Dana—Fairfield County Minerals. 
aspect. As shown in the figure the three planes, whose 
several inclinations are almost identical, have their common 
this is the true explanation is proved by the optical examina- 
tion. The cleavage is basal, nearly perfect. 
The angles (supplement) accepted as the basis for calculation, 
are as follows :— 
Cap 001.111 = 58° 40’ 
exd 001.201 = 58°31’ 
pap TPA ALL: =e: 1007: 287 
Caleulated from these the elements of 
the crystal are :— 
c (vert.) b B 
8201 “BITS 1:0000 or 89° 51” 
1:4190 1-000 17303 
The get taken for the crystal is that ipa 
which exhibits most strikingly its close approximation to the 
rhombohedral form. If it were desired to make the plane d 
the unit orthodome 101, then the plane p would have the sym- 
bols 111 and 111, and the elements of the crystal would be :— 
B=78° 11’; ¢ (vert.)=1-1422, b=0°578, d=1-000. : 
The observed planes have already been given; they are :— 
ce 001 0. @ 21: 24. p il il. 
The calculated angles and those measured (on two crystals) 
ar 
Calculated. Measured 
qd) @) 
cad 001,201 = 58°31 58° 31’ 
Maat fetus *58° 40° 
— 1001 iit # ies 8 oe" ot" 
pap 1.111 = 95° 93° #95° 23” 95° 25” 
T11 . 201 a 95° 207 95° 15” 
es — = ios 9F ° ° 
_- i iil . 201 ote 95° 16 95° 18” 
they lay, since the only sections transparent enough for | 
examination were destitute of the other crystalline planes. _ 
aN Se gle as aa oe 
