Carbonate of Lime

A crystal is denominated compound, when several of one form combine to make one of another. This happens rather rarely in most substances, but is frequent in Carbonate of Lime, the lenticular or equiaxed variety more particularly is grouped so as to form other crystals. The upper figure in this plate is, however, a more distinct example than usual, yet is easily comprehended. In it many equiaxed rhombs are piled together, so as to form a crystal resembling the metastatic variety. In the other figure the pyramids formed of similar rhombs are so acute as almost to produce columnar crystals. Specimens similar to the upper one are found in the county of Durham, North Wales, &c., accompanied by lenticular crystals of brown Iron Spar, The lower specimen represents part of a specimen, the matrix of which is Fluor; it is from Westmoreland. Modifications of different substances may be understood from these examples, although compounded of others very different.

Sulphate of Barjtes, tab. 380, is compounded of nearly primitive crystals, which is usually the case with this substance, though very rarely with Carbonate of Lime.