Command
higher prices there than in London, but inferior grades are lower.
Large pale turquoises often veined or spotted with white, are exported
a good deal to India and sold there quite cheaply. The mines are farmed
out by the local authorities for a yearly payment of £5,000, and the
lessees in turn rent most of them to other parties.
VESUVIANITE (CALIFORNITE). CALIFORNIA.
In Bulletin No. 202 of the United States Geological Survey.a
Prof. F. W. Clarke and Mr. George Steiger have given full analyses of
the compact variety of vesuvianite. called by the writer californite,
from Siskiyou and Fresno counties, Gal., and also of the peculiar white
garnet found associated with it at the latter locality.b The
analyses are recalculated and reduced to a uniform type by eliminating
impurities and replacements, and an attempt is made to deduce
structural formulas. The white mineral proves to be a true garnet,
containing as an impurity about one per cent of calcium carbonate. The
variations in these and many other analyses of vesuvianite lead
Professor Clarke to the view that this mineral may be a mixture of
several closely related molecules. These Californian varieties, and
others also, conform very well to the expression
This differs slightly from the formula previously deduced by Dr. Clarke, viz:
which
serves well " for the average composition of the species, but does not
fit the extremes." Hence the suggestion of a mixed constitution.
Vesuvianite
should be considered as a basic orthosilicate belonging to a group of
which garnet is the normal type, with epidote and the scapolites as
other members. Their formulas are closely related; they originate
similarly from contact metamorphism. They all alter in much the same
manner, and yield similar or even identical derivatives.
OBSIDIAN. MEXICO.
In the
report of this Bureau for 1900 was given an account of the great
prehistoric obsidian mines in Mexico, near Pachuca, in the State of
Hidalgo, as visited and described by Prof. W. H. Holmes. At this point,
though the material exists in such quantity, yet no outcrops could be
seen, all being buried under the heaps of debris and fragments left by
the ancient workers. A recent communication to the author from Mr. J.
M. Hamilton, of Tequisquiapan, in the State of Queretaro, describes
another locality some 00 or 70 miles west of the former, where a
closely similar obsidian occurs abundantly, but does not appear to have
ever been mined or developed, and where the outcrops are entirely
accessible. The locality is near the border of the States of Queretaro
and Hidalgo, on a range of low hills east of the San Juan River,
between the crossing of that stream by the Mexican Central Railroad,
at San Juan del Rio, and by the National Railroad of Mexico a few miles
below.
