Crystallized Quartz

Perhaps this is one of the most remarkable crystallizations ever observed in Quartz. As the ends of the primitive rhombs—see tab. 41—are so scarce, this specimen is the more curious, having them dispersed about it. It is particularly so, for their being as it were nearly mackled, or in pairs, making a bifid-ended crystal, which is partly a series of these depositions, undulating in a somewhat step-like manner, as if formed on each other, sometimes with scarcely any prismatic sides, except at the lower ridge of the opposite rhombs. Sometimes they are nearly trifid—see figures 1, 2 and 3. Besides these there is a very odd formation in two places, much resembling the semicircular ends of bivalve shells, partly gaping, like the fruit of some Banksiæ, for instance of Banksia conchifera of Gærtner. These have smaller crystals on their outside, like the others; they are rather concave within, and a little convex without. This specimen was sent me by my kind friend John Slackhouse, Esq., among other favours, from Cornwall. The whole specimen is Quartz, a little coloured by Oxide of Iron, although at the back in some parts it is darker, and there are one or two crystals of a red tint with triedral ends, which correspond with the characters of the Eizen-kiesel of the Germans—see tab. 219. This odd mackled formation of Quartz it was the more necessary to figure, as the rhomb referred to was scarcely known, and much less so deceiving a crystal as this, if I may so call it, which has but little of the usual appearance of Quartz.