MIL A. E. TUTTOX OX A COMPARATIA’E CRYSTALLOGRAPHICAL STUDY 
25(i 
Hal;)it: Short prismatic to tabular. 
Axial angle : ^ = 75^^ 42'. 
Ratio of axes : « ; 6 : c = 0'7485 : 1 : 0'5031. 
Forms observed : « = J 100}- go 4^ co ; J> — 1 010 J- go F co ; e = [001 ] oP ; 
2 ) = [no} oD P; q = -!011}P 00 ; r' = {201} + 2P oc ; a' = [Til} + P. 
Tlie results of the measurements are set forth in the accompanying table of angles. 
The crystals were distinguished by the preponderating development of the c and 
[) faces. Faces of tlie form r were generally present, but small, while the q faces 
were even smaller and frequently absent altogether. A typical crystal is sho^vn later 
in fig. 1 (p. 274), in the discussion of the comparative habits of the three magnesium 
salts. Many of the crystals resembled fig. 21 in the double sulphate memoir [loc. 
cit., p. 384), except that there was no trace of h or o'faces. It occasionally happened 
that while one r' face was very small, the other one was relatively largely developed. 
The orthopinacoid a was discovered fairly well formed on one of the crops investi¬ 
gated, but was absent on the other crops. A trace of the hemi-p^u’amid o' was 
observed on one crystal, but the signal images afforded were not adequately good for 
the purposes of measurement. 
Morphological Angles of Potassium Magnesium Selenate. 
A) 
igle measui’ed. 
Xo. of 
nieasui e- 
meiits. 
Limits. 
Mean 
oliserved. 
Calculated. 
Differ¬ 
ence. 
' (JC 
100 
001 = ji 
o 
/ o / 
o / 
o / 
75 42 
' 
as 
= 
100 
101 
— 
— 
— 
46 30 
— 
sc 
= 
101 
001 
— 
— 
29 12 
— 
J 
o' 
= 
001 
201 
21 
62 
55— 63 4 
62 58 
62 53 
5 
■ 
(■•s' 
= 
001 
101 
— 
— 
— 
38 1 
— 
/ / 
s r 
= 
101 
201 
— 
— 
24 52 
— 
ra 
= 
201 
TOO 
-- 
— 
— 
41 25 
— 
r'c 
= 
201 
001 
21 
116 
57—117 8 
117 2 
117 7 
5 
f "j" 
100 
110 
2 
35 
53— 35 55 
35 54 
35 55 
1 ' 
1 ri' 
= 
110 
120 
— 
— 
— 
19 28 
- i 
j j/h 
= 
120 
010 
— 
— 
34 37 
— 
'11 '^' 
= 
no 
010 
2 
54 
5— 54 7 
54 6 
54 5 
1 
■ i VP 
= 
110 
no 
17 
71 
42— 71 57 
71 50 
•X- 
— 
= 
110 
no 
18 
108 
0—108 21 
108 10 
108 10 
0 
f '■? 
001 
on 
28 
25 
53— 26 8 
26 0 
* 
_ 
qb 
= 
on 
010 
3 
64 
0-- 64 6 
64 2 
64 0 
o 
L'i'i 
= 
on 
on 
G 
128 
0--128 3 
128 1 
128 0 
1 
' no 
100 
111 
__ 
_ 
49 43 
_ 
Oq 
= 
111 
on 
— 
— 
— 
27 27 
— 
aq 
= 
100 
on 
— 
— 
77 10 
.... 
qu 
= 
on 
Ill 
-- 
— 
34 16 
— 
da 
K 
= 
Til 
TOO 
— 
— 
— 
68 34 
— 
