Crystallized Carbonate of Lime, var. equiaxed

This crystal is formed of six rhomboidal faces the angles of which are 114° 18′ 56″, and 65° 41′ 4″, forming a very obtuse rhomb, the axis of which is equal to that of the rhomb which is encloses. Haüy, v. 1. 133.

These and their modifications are found plentifully in Durham and Cumberland, according to the specimens sent me by the Rev. Mr. Harriman and Mr. Oliver. I have had fine specimens from Newcastle by favour of Mr. Woodhouse, found in coal mines. They occasionally occur wherever other calcareous substances are found.

The upper figure is part of a fine specimen with clearer crystals than usual, for they generally incline to a milky hue. They frequently stand on their edges, or are as it were thrown about in different directions, on which various matrices. This is on dark grey lime-stone, with blend^* and galæna^†. The first is confusedly crystallized, which commonly happens; the latter more regularly so, in cubes with the corners truncated, or a cubo-octoaëdron, as Haüy rightly terms it.

The lower figure has smaller crystals, roughish towards the edges, as if not quite finished. The roughness proceeds from the edges of the molecule, or from spaces where there seems something wanted to finish the faces and make the surfaces even. The crystals are somewhat striated towards the centre, and are loosely fixed among light purple fluor and galæna.