1919.] 
Departmental Reports. 
47 
price appears to have advanced, as indicated above, to over 5s. per unit 
for all ore over 40 per cent., provided silica is low. On the 14th May last 
the quotation at San Francisco was approximately 5s. 3d. to 6s. 4d. per 
unit for chrome-iron ore with over 38 per cent, of chromium sesqui- 
oxide. This corresponds to a range of 5s. lOd. to 7s. per long-ton unit, 
or £14 11s. 8d. to £17 10s. per ton of 50-per-cent. ore. 
MICA. (By P. G. Morgan.) 
Mica of various kinds is a common rock-constituent in New Zealand, 
as in other parts of the world. Large plates of mica are known to occur in 
only two localities, one of which is Dusky Sound, south-western Otago, 
and the other Charleston, south of Westport. Practically nothing is known 
about the Dusky Sound occurrence except that the discovery was made 
many years ago by the well-known prospector William Docherty. Several 
samples of fair-grade mica collected by Docherty are in existence. One of 
these is in the Waihi School of Mines collection. 
The occurrence of mica at Charleston was known many years ago, and 
the analysis of a sample in the Otago Museum was published by Professor 
Liversidge in 1878.* During 1911 and 1912 a large pegmatite vein near 
Charleston was worked for its mica content. Estimates of the amount of 
mica obtained vary from 2 to 6 tons. This, or part of it, was exported to 
England, but it is understood that much of the material shipped was not 
in the form of merchantable sheets, and was merely scrap. The workings 
were examined in 1913 by Morgan and Bartrum,]* who report that some 
of the mica is cross-grained, and all seen by them dark-coloured. The 
material near the surface was affected by weathering, but this defect would, 
of course, disappear in depth. Plates measuring as much as 6 in. by 4 in. 
could be obtained, but the writers mentioned were of opinion that the 
proportion of sheet mica to barren rock was too small to enable the peg¬ 
matite to be profitably worked unless richer patches could be found. Since 
the publication of their report the price of mica has more than doubled, 
and for the time being the opinion mentioned may possibly not hold good. 
Prices of Mica. 
In July, 1914, the London prices of muscovite mica were approximately 
as follow :■— 
Size. 
Area of Rectangular 
Plate obtainable. 
Price per Pound, according to 
Quality. 
No. 6 
Square Inches. 
1 to 3 
s. d. s. d. 
0 1| to 0 5f 
No. 5 
3 to 6 
0 5J to 2 4 
No. 4 
6 to 10 
2 3 to 4 8 
No. 3 
10 to 14 
3 6 to 7 9 
No. 2 
14 to 24 
5 6 to 8 3 
No. 1 
24 to 36 
6 6 to 9 0 
* Notes on some of the New Zealand Minerals in the Otago Museum. Trans. 
N.Z. Inst., vol. 10, pp. 497-98, 1878. 
t N.Z. Geol. Surv. Bull. No. 17, pp. 124-25, 1915. 
