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242 PRECIOUS STONES.
powdered
Lapis Lazuli as a dressing for pustules and boils, for it is possible
it may have some antiseptic action when moistened. Since the mineral is
imbedded in the carbonate of calcium, Calcite, it follows that on
applying hydrochloric acid, effervescence is produced. Also the
presence of the sulphide of iron would render it liable to
decomposition if not kept dry. With regard to distribution, it seems
more than likely that the localities mentioned by the old writers
(Medea and Ethiopia) may have simply been trading localities, and not
places where the stone was actually to be found. On the upper part of
the river Oxus, to the north of the Hindu Kush, it is found in a
limestone rock, and here it has been worked from very ancient times,
and the method still adopted of winning it seems the same as it was
then, namely, by heating the rock by a fire and then suddenly cooling
it with Mater, and thus causing the rock to split up. Much of the Lapis
Lazuli from this locality goes to the great annual fair at Nizhni
Novgorod, in Russia.
At
the western extremity of Lake Baikal it occurs to the south of Kultuk
in a crystalline limestone near the meeting zone of granite and gneiss
; and to the west of Kultuk in a granular limestone in granite a good
deposit exists; and here an improvement in quality of the material is
observed as the depth of the workings increases, so that the rich
colour is probably not due to the effect of weathering. In the Andes,
in Chile, it occurs in a metamorphosed limestone underlying a granite
rock, and in the detritus of these rocks. It is associated with Ruby in
Burma.
It is cut as a flat plaque, or en cabochou; more often it is worked into vases and other small ornamental objects,
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