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Updated: October 5, 2026
When a fluid mass of any mineral or metallic substance is made to congeal by sudden cooling on the outside, while the mass within is fluid, a cavity is thus sometimes formed by the contraction of the contained fluid; and in this cavity are found artificial druzen, as they may be called, being crystallizations similar to those which the mineral cavities exhibit in such beauty and perfection.
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 . 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.