Ferriferous Carbonate of Lime
This is part of a superb Specimen collected last summer by John George Children, Esq. at Audlim mine, about eight miles from Bodmin, Cornwall, and is somewhat the more remarkable as it used to be said that Carbonate of Lime was not to be found in Cornwall, The whiter part of the specimen is a cavity handsomely filled with crystallized Carbonate of Lime of a very uncommon modification, being nearly an hexaëdral plate with the equiaxe and primitive bevellings, if I may so call them. It is rather remarkable that the external surfaces of these crystals are whitish, and the inside of a rich dark brown, as the darker surrounding part shows*. Tab. 62. British Mineralogy is nearly of the same nature, but under common circumstances grows blacker by exposure to the air.
This specimen has many other curious circumstances of change and position of mineral substances attending it; viz, the redder parts are a sort of Carnelian Quartz, somewhat approaching Chalcedony, coloured by a rich Oxide of Iron, and this is sometimes covered by Cachalon: see British Mineralogy, tab. 111.
Besides this there are yellow spiculatcd tubes, almost crystallized, radiating, &c. These are to be seen as forming over wire-shaped Pyrites; see Brit. Min tab. 162. This has decomposed in some parts, leaving the hollow where it has been with enough to show the appearance of a wire, as the fracture in some parts on the opposite side shows; perhaps it may be between Eisen Kelsel; or the German Iron Flint, and Carnelian. Some gray Cachalon covers the Carnelian in the hollow as represented at the top of the figure. The yellower Quartz seems to be coloured by yellow oxide of Iron, probably the decomposed Pyrites.
- * This specimen has probably been broken from an opposite piece, and was given to the worthy Mr. Rashleigh.