But to understand this
specimen, something must be premised with regard to the nature of fossil
alkali.
The fossil alkali crystallises from a dissolved state, in combining
itself with a large portion of the water, in the manner of alum; and,
in this case, the water is essential to the constitution of that
transparent crystalline body; for, upon the evaporation of the water,
the transparent salt loses its solidity, and becomes a white powder. If,
instead of being gently dried, the crystalline salt is suddenly exposed
to a sufficient degree of heat, that is, somewhat more than boiling
water, it enters into the state of aqueous fusion, and it boils, in
emitting the water by means of which it had been crystallised in the
cold, and rendered fluid in that heated state. It is not possible to
crystallise this alkaline salt from a dissolved state, without the
combination of that quantity of water, nor to separate that water
without destroying its crystalline state.
But in this mineral specimen, we have a solid crystalline salt, with
a structure which, upon fracture, appears to be sparry and radiated,
something resembling that of zeolite.
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