Quartziferous Carbonate of Lime. Crystallized Sandstone

This specimen shows that the strong tendency of some substances to crystallize often overcomes what might reasonably be thought great obstructions. It is a mixture of Carbonate of Lime with Silicious sand in the form of the inverse rhomb^*, and is not known in any perfection but at Foatainbleau, where it is tolerably abundant, either in single crystals, or variously grouped. It is certainly extraordinary, as it sometimes does not contain in an hundred parts above 371/2 of Carbonate of Lime, the crystallization of which governs the form, the remaining 621/2 being sand. We do not know of any specimens of Carbonate of Lime in a nearly pure state crystallized so finely in the form of the inverse rhomb; although we understand there are some crystals found at Fontainbleau, that are half of them pure Carbonate of Lime, and half mixed with Sand. The crystals seldom vary from the true measure of their angles 102° 30′ and 77° 30′, and are generally very neat. The large rhomb on the present specimen is rather out of shape, and there is a curious embossment on one of the relieved crystals, and one of those on the left hand of the print has a sign of truncated angles, possibly rare, as I have not seen it on any other specimen. The whole is so extraordinary, that I despair of seeing such in Great Britain, and therefore consider this figure the more necessary.