Carbonate of Lime

This singular modification of Carbonate of Lime came from the neighbourhood of the Ecton-mine, Staffordshire, having been gathered by W. E. Sheffield, Esq., who was so good as to favour me with the use of the specimen. The depth of two of the facets of each pyramid, or the want of a proper supply to give them a proportion to the others, is a sort of deception, as they are nearly the same with the foregoing, except one or two additional facets, and the diagonal mackling. Thus the whole is shortly accounted for; and as these are extremely rare specimens, I was glad of an opportunity to show them, and to explain so instructive a lesson in Crystallography.

The gangue is chiefly of variegated Pyrites, but in another specimen possessed by my friend there is much Sulphate of Barytes with the faces as in the geometrical figure at the bottom of tab. 72, giving them a singular sharp-edged appearance; and the modifications of the Carbonate of Lime are rather more mixed, or have the other ends of the crystals appearing in some parts beyond the mackling, rather irregularly, I am the more gratified in having the use of these specimens, as the mackle in such a direction in Carbonate of Lime has not, to my knowledge, been noticed before, nor is it mentioned by Haüy, being in itself very puzzling.

The place of intersection is parallel to one of the faces of the equiaxe rhomb, or to the edge of the nucleus, and corresponds with the diagonal fractures that may be obtained from some varieties of Carbonate of Lime.