80 
Rex T. Prider. 
mound. It consisted of a mixture of white fibroferrite (predominant), yellow 
copiapite, and colourless melanterite. None of this material remained at 
the time of my visit in April, 1941 (possibly having been dissolved by rain, 
as these minerals are all w’atcr-soluble) and the only ferric sulphate minerals 
seen w'ere from encrustations on the surface of small heaps of spoil from shallow 
holes which had been dug on the surface of the mound — such material con- 
sisted largely of copiapite and melanterite with no libroferrite. Several 
samples were taken from the encrustations: ( 1 ) of moist yellow material, 
and ( 2 ) of dry earthy yellow material. 
Figure 1. 
General view of the niouiul at Yetar Spring. The figure on right 
gives tlie scale. 
The f(‘rric sulphate minerals are : — • 
A. Fibroferrite . — Present only in the sample collected by Mr. Burgess. 
It was identified optically and the determination checked by qualitative 
chemical tests. The properties of this mineral are : — 
White in colour in the mass and soluble in cold water, the resultant 
solution giving positive reactions for Fe"' and SO 3 only. Yields water 
and then SO 2 in the closed tube. Under the microscope it is seen to be 
in tiny colourless acicular forms with Z [| length, y = 1*600 + *002 and 
oc = 1 • 553 + * 002. These refractive indices are somewhat higher than 
those given by Larsen and Bennan (1934, p. 103) for fibroferrite, viz., 
y ~ 1*575 and oc 1*533. 
None of the Yetar Spring fibroferrite could be obtained free from copiapite 
and no quantitative analysis has been made. The small lumps of white 
fibroferrite (about J inch diametei’) when broken are seen to contain a central 
core of copiapite. 
B. Mekmterite was identified optically from the samples collected by both 
Mr. Burgess and myself. My samples consisted entirely of copiapite and 
melanterite. In the damp material (sample 1) melanterite was more abundant 
than in the dry sample (No. 2) which consisted predominantly of copiapite 
with lesser amounts of melanterite. An estimation of ferrous iron m the 
moist material after drying in a desiccator over calcium chloride gave FeO 
