260 BULLETIN OF THE IMPERIAL INSTITUTE
Large
blue stones and coarse corundum crystals are obtained in some places.
Gravel yielding 1/2 oz. of " parcel blues " per load can generally be
worked without loss, but if less than a foot of gravel has to be mined,
a return of 1 oz. per load may be necessary for profitable working.
In April 1913 the prices realised for stones were 55. to £5 per dwt. for fancy stones; £2 10s. to £6 per oz. for large blue stones; 35s. per oz. for parcel blues; 7s. 6d. per oz. for small blues; and 3s. to 3s. 6d. for machine stones. Pieces of opaque corundum over 1 oz. sold at 6s. to 85. per oz. An inferior or flawed variety of stone sold as "schneid" at 1s. 6d. per lb.
Much
of the corundum and sapphire found at Anakie has proved to be valuable
for mechanical purposes, and when free from fracture, though it may be
useless for ordinary gem purposes, can be made into small bearings and
pivots for parts of machines running at high speeds.
It
is noteworthy that there has been a strong demand for dark violet-blue
stones. These stones are so dark that they appear quite opaque in dull
weather, and ean only be identified on a cloudless day. In the larger
sizes (up to 3 oz. in weight), stones of this colour sell for as much
as £5 per oz., although they yield a black stone when cut locally, and
it is suspected that the Germans have some method whereby they can
modify the colour. It may be suggested that this is probably done by
the simple method of heating the stone. Many minerals, such as, for
instance, smoky zircon, have their colour modified and their
transparency greatly increased after having been heated to redness;
and a specimen of Anakie sapphire examined at the Imperial Institute
showed a greatly increased transparency as the result of this
treatment.
Output
In
the year 1900, the first year for which the output of Anakie sapphire
was reported, the estimated value of the output for the year was given
at £2,500. Since that date there has been a substantial increase, and
in 1913 the year's output reached a value of £43,292. As already
pointed out, however, the industry was practically brought
