Siderite is a difficult stone to facet, but cut gems of great beauty have been fashioned, especially from Portuguese rough.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Hexagonal (R). Crystals rhomb shaped; also massive, granular; globular; oolitic.|
|Colors||Pale yellowish brown. pale yellowish, pale green, greenish gray, yellowish gray, grayish brown, reddish brown, blackish brown; rarely almost colorless.|
|Luster||Vitreous, pearly, silky, dull.|
|Cleavage||Perfect rhombohedral. Brittle.|
|Stone Sizes||Siderite is not usually cut as cabochons because the massive material is not attractive, and the perfect cleavage makes cutting very difficult. Faceted siderite is rare and stones are usually small (1-5 carats). National Museums of Canada (Ottawa, Ontario): 2.60. 2.25 (light brown, Quebec, Canada).|
Series to Rhodochrosite (MnCO3) and Calcite (CHCO3).
Optics: o= 1.873; e= 1.633.
Occurrence: A widespread mineral in sedimentary deposits; hydrothermal ore veins; also in pegmatites; basaltic rocks.
Colorado; Connecticut; Idaho.
Austria; France; Germany; Italy
Minas Gerais, Brazil: large and fine crystals.
Mt. Ste. Hilaire, Quebec, Canada: brown rhombs up to 15 inches on edge.
Panesqueira, Portugal: fine light brown crystals, some transparent.
Ivigtut, Greenland: rich brown, gemmy-looking crystals in cryolite.
Cornwall, England: greenish crystals, some transparent, known as chalybite.
Comments: Siderite is a difficult stone to facet, but cut gems of great beauty have been fashioned, especially from Portuguese rough.
Name: From the Greek rideros (iron) in reference to the composition. Chalybite is from the Greek of steel, referring to the Fe and C content.