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GEMS.
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are
of an iridescent green colour which resembles the eye of a fish ; which
often, in very thin lamina, becomes by reflection a pale rose colour.
This gem is remarkable for its brightness, which may compare equally with that of pearl and glass.
It is very easily worked, having three cleavages, and has double refraction.
Its cleavage is perfectly concave.
Being altogether destitute of electricity, it does not act on the magnetic needle.
When exposed to the action of the blow-pipe it melts into a transparent white glass.
Its specific weight is 2-5. The heat, 0.1861.
The analysis of adularla gives
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Although
adularla scratches rock crystal, it is less hard than quartz. It is
very difficult to specify its precise hardness, as the same piece
contains portions which, being iridescent, are naturally soft ; others
of a milky whiteness, which are harder, and, lastly, others which
surpass the rock crystal in resistance.
This
substance, which has so many peculiarities, and is so specially prized
for the pearl-white reflections which seem to move about inside the
stone when it is turned,' frequently owes more to the art of the
lapidary for its admirable effects of light than to its natural
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