Fibroferrite and Copiapite from Yetar Spring, near Chidlows. 81 
7 • 38 per cent, (as compared with FeO 4 * 50 per cent, in the naturally dry sample 
No. 2 — see Table 1 below). The melanterite occurs as colourless weakly bi- 
refringent granules with refractive index 1 • 48. 
C. Copiapite is the most abundant constituent of the naturally dried 
material (sample 2). It is earthy yellow material, soluble in cold water, yield- 
ing a brown acid solution. Under the microscope it is seen to be in micro- 
scopic yellow non pleochroic plates with high birefringence and y = 1-578. 
An analysis was made of the copiapite-rich sample (No. 2) and the result 
is shown in Table 1. 
Table 1. 
Analysis of Copiapite-rir.h Material {Sample 2). 
Analysis on material dried in desiccator over calcium chloride for seven days. 
Insol. (1) ... 
• 
/o 
0*88 
Mol. 
prop. 
Melanterite. 
Copiapite. 
No. of Metal 
Atoms on basis 
of 6 S. 
FeO 
4-50 
•063 
■063 
, . • 
Fe/J, ... 
21 -39 
-134 
•134 
3-78 
AI 0 O 3 
Nil 
, • • 
Cab 
Tr. 
MgO 
1*27 
■032 
■032 
0-45 
K 2 O 
0-25 
-002 
•002 
0-06 
Na.^O 
2-17 
■035 
•035 
0-99 
SO, 
39-17 
•490 
■063 
•427 
6-00 
Hob( 2 ) ... 
30-37 
1-687 
-441 
1*246 
35-10 
Of 
Tr. 
... 
. • . 
• • . 
. . . 
100-00 
Anal. • R. T. Prider. 
(^) Insoluble in cold water. 
(^) By difference. A separate determination on another sample gave “ loss on ig- 
nition ” 65*82 per cent. 
On the assumption that all of the FeO is in the form of melanterite the 
residue (copiapite) has the formula (Na 2 , Mg)o. 97 (OH)i. 94 . 
- 00 - 
16-58 H 2 O, which agrees fairly clo.scly with the formula X( 0 H) 2 .Fe"' 4 (S 04 )g. 
n H 2 O suggested by Peacock (see Berry, 1939, p. 182). Following the nomen- 
clature proposed by Berry (1939) this mineral would be a soda-magnesio- 
copiapite. 
THE ORIGIN OF THE MOUND AND THE ASSOCIATED FERRIC 
SULPHATE MINERALS. 
The mound surrounding the spring has apparently grown by addition of 
material from below. It ajopears most probable that the ferric sulphate 
minerals have been derived from a mass of pyritic material lying below the 
surface. The surroimding country (although outcrops are scarce in the 
imnu'diate vicinity of the spring) is made up of Pre-Cambrian granitic rocks 
which would not be expected to contain any appreciable amount of pyrite — 
nevertheless pyritic masses are known to occur in the Darling Range granite, 
for example, at the Canning Dam quarry I have observed a well developed vein, 
several feet wide, of crushed granite heavily mineralised with pyrite. Again 
there may be a dolerite dyke carrying pyrites below the mound spring. Material 
<lerived from such a mass of decomposing pyrite lias evidently been carried to 
the surface by the spring waters and deposited in the porous diatomite of the 
