450 Mr. Brooke on crystallized native Oxalate of Lime. 
that as one of the primary planes, and there are other clea- 
vages parallel to M, and to c of fig. 2. Most of the crystals are 
twins, and remarkably symmetrical in their form. Fig. 3 is a 
projection of the terminal planes ; and fig. 4, a projection of the 
twin crystal in profile, the relation of which to fig. 2, and the 
other figures, is rendered sufficiently obvious by the corre- 
sponding letters. All the planes are bright and perfect except 
M, which is striated by its alternations with u ; and f which 
is also striated parallel to the edge between yand f. 
Fig. 3. 
The following are the laws and measurements of the planes, 
for taking the trouble of calculating which I am indebted to 
the kindness of my friend Professor Miller of Cambridge. 
Fig. 2. Fig. 4. 
a = 127 25 
c = 90 
h = 109 28 
5 = 136 48 
/ = 143 4 
a on s = 154 19 
/ = 1"^'3 
c = 
u 
c 
a 
V 
./ 
18 
142 36 
160 45 
129 42 
111 37 
128 4 
136 48 
142 15 
Fracture 
S' 
f = 
Very brittle. J^racture con- 
choidal. Hardness rather less 
b 101 41 than calcite. Spec. grav. 1*833. 
Colourless. Transparent to opake. Lustre similar to that 
of sulphate of lead. H. J. B. 
