In these cavities of the solid granite rock, where crystal is found
regularly shooting from a basis which is the internal surface of the
cavity, we find the other constituent substances of the granite also
crystallised. I have those small cavities, in this rock, from the island
of Arran, containing crystal, felt-spar, and mica, all crystallised in
the same cavity[34]. But this is nothing to the _druzen_ or crystalline
concretions, which are found in a similar manner among metallic and
mineral substances in the veins and mines; there, every species of
mineral and metallic substance, with every variety of mixture and
composition, are found both concreted and crystallised together in every
imaginable shape and situation.
[Note 34: The Chevalier Dolomieu makes the following observation.
Journal de Physique, Juillet 1791.
"J'ai ete etonne de trouver au centre d'un enorme massif de granit, que
l'on avoit ouvert avec la poudre pour pratiquer un chemin, des
morceaux, gros comme le poing et au dessous, de spath calcaire blanc,
tres-effervescent, en grandes ecailles, ou lames entrecroisees.
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