82 
MUSEUM BULLETIN NO. 27. 
The crystals, which, as already noted, are perfectly colourless and 
transparent, are mostly very minute, but some measured up to one 
centimetre in diameter. The habit is invariably tabular parallel to the 
base, and the crystal plates are quite thin, even the largest crystals not 
exceeding 2 mm. in thickness. They are generally doubly terminated. 
Irregularities on the basal plane in all the crystals measured indicate that 
parallel growth is very prevalent. 
Owing to the habit, the basal pinacoid is by far the most prominent 
form on all the crystals. Otherwise, they are of two types, characterized 
in general by the presence or absence of the prism of the first order, 
m(1010). In the first type, the principal forms present, in addition to 
the basal pinacoid, are the prism of the first order m(10l0), and the two 
pyramids of the second order s(1121) and v(1122). Other forms noted 
on these crystals, in the order of their relative development, are the first 
order pyramids, y (2021), x(1011), and r(l0l2); the third order pyramids, 
fi( 2131), n(3141), and o(3142); and the third order prism, h(2130). In 
addition to these, the first order pyramid, «(3032) was noted as small 
faces on some of these crystals. 
In the second type, the largest form, after the base, is the first 
order pyramid, r(1012); the second order prism, a(1120) is present as 
narrow faces, but the first order prism is lacking. 
A complete list of forms observed, together with the measured and 
- calculated angles, is given below: 
Crystal Forms of Apatite, 
Letter 
Symbol 
Measured 
Calculated 
Dana 
Gold- 
schmidt 
9 
P 
9 
p 
0001 
lOTO 
b. , 
1120 
h 
h 
2130 
19° 06' 
90° 00' 
19° 06' 
90° 00' 
1012 
0 00 
23 00 
0 00 
22 57 
lOll 
0 00 
40 18 
0 00 
40 16 
3032 
0 00 
51 46 
0 00 
51 48 
. . . . . V. 
2021 
0 00 
59 30 
0 00 
59 27 
1122 
30 00 
36 16 
30 00 
36 16 
8. . 
1121 
30 00 
55 45 
30 00 
55 43 
n 
3lll 
13 52 
71 54 
13 54 
71 5? 
. . 0 . 
3142 
13 52 
56 43 
13 54 
56 47 
2131 
19 00 
66 00 
19 06 
V 
65 57 
