110 CONTRIBUTIONS TO MINERALOGY. [bull. 262. 
The combinations seen on the six crystals are as follows: 
No. 
1 
No. 
2 
No. 
3 
No. 
4 
No. 
5 
No. 
6 
California 
California 
Arizona . . 
New York 
New York 
New York 
b, 
a, 
!, 
—, 
Til, 
9, 
n, 
—j '- 
b, 
a, 
1, 
K 
m, 
9, 
ft, 
d, - 
b, 
a, 
I, 
:; 
5 
9, 
9, 
y 
> 
> 
-, 
a, 
I, 
— , 
— , 
9, 
> 
) 
Fig. 8 shows three of the crystals. A is from California; size, 
1 mm. X i mm. B is from New York; size, 1 mm. X i mm. C is from 
Arizona; size, 1 mm. X 1 mm. 
The following table gives the calculation of the forms of dumortierite 
based on the elements given in this paper. The table corresponds to 
the forms given in Goldschmidt's Winkeltabellen. 
a =.8897 
lga=9.94924 
lga o =0.11202 
]gp =9.88779 
a =1.2943 
p =.7723 
c = .6871 
lgc= 9.83702 
lgb = 0.16298 
lgq o =9.83702 
b =1.4554 
q =.6871 
No. 
Let- 
ter. 
Sj 
m. 
<*> 
P- 
£ 
V 
f. 
-0- 
X 
(Prism) 
x: y. 
.'/• 
d=tg p. 
Mil- 
ler. 
gdt. 

, 
/ 
c 
, 

, 

, 
1 
1 
b 
010 
0oo 

00 
90 00 

00 
90 
00 

00 
90 00 

oc 
00 
2 
a 
100 
ccO 
90 
00 
90 00 
90 
00 

00 
90 
00 
00 
00 

OO 
3 
I 
120 
oc2 
29 
07 
90 00 
90 
00 
90 
00 
29 
07 
60 53 
.5570 
00 . 
00 
4 
VI 
110 
OO 
49 
01 
90 00 
90 
00 
90 
00 
49 
01 
40 59 
1.1510 
(X 
00 
5 

320 
fOC 
59 
47 
90 00 
90 
00 
90 
00 
59 
47 
30 13 
1.7170 
OO 
OO 
6 
n 
210 
2 co 
65 
23 
90 00 
90 
00 
90 
00 
65 
23 
24 37 
2. 1825 
OO 
OO 
7 
d 
102 
5O 
90 
00 
21 07 
21 
07 

00 
21 
07 
00 
.3862 

0. 3862 
8 
V 
203 
10 
90 
00 
27 14 
27 
14 

00 
27 
14 
00 
.5147 

.5147 
The minerals andalusite, sillimanite, staurolite, and dumortierite 
possess certain properties that are very much alike. They are all 
orthorhombic, their axial ratios are similar, their principal constitu- 
ents are silica and alumina, and in many ways these minerals can well 
be grouped together. Using the word isomorphous in its general 
loose sense, these minerals are isomorphous. A comparison of their 
axial ratios is given below: 
a. 
c. 
Andalusite 
[ .9861 
. 7025 
Sillimanite 
.970 
(?) 
. 6942 
Staurolite 
. 9795 
Dumortierite 
! . 8897 
. 6871 
