Siderite Value, Price, and Jewelry Information
Siderite is difficult to cut, but this light brown collector's gem has yielded faceted pieces of great beauty.
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.|
|Fracture||Conchoidal to uneven|
|Transparency||Transparent to opaque.|
|Optics||o = 1.873; e = 1.633. Uniaxial (-).|
|Etymology||From the Greek sideros for “iron,” in reference to its composition.|
|Occurrence||A widespread mineral in sedimentary deposits; hydrothermal ore veins; also in pegmatites; basaltic rocks.|
Siderite forms three solid solution series. It’s the iron (Fe) analogue in a series with manganese (Mn) dominant rhodochrosite. It also forms the Fe-end of a series with zinc (Zn) dominant smithsonite, as well as with magnesium (Mg) dominant magnesite.
These other series members have attracted some interest as cabs and rare transparent faceted pieces, despite their low hardness. On the other hand, gem cutters don’t typically cab siderites. In addition to low hardness and perfect cleavage, the massive material suitable for cabbing is unattractive. (Evidently, the surge of popular interest in earth tone gems hasn’t yet reached siderites). Nevertheless, as faceted pieces, these golden and honey-colored gems would make unusual, prized additions to any gem collection. In particular, Portuguese rough has yielded beautiful faceted stones.
Siderite has been used as an iron ore and for steel production. Material from Cornwall, England has been called “chalybite,” after the Greek word for steel, referring to its iron and carbon content.
Scientists have synthesized siderite to study its use for the removal of fluoride and arsenic from water. The synthetic material also has applications for agronomy as well as lithium ion batteries. However, this synthetic material has no known jewelry use.
Due to their similar colors and hardness, siderites may be misidentified as rhodochrosites, smithsonites, or magnesites. Nevertheless, gemologists can distinguish them based on differences in specific gravity as well as optical properties.
Panesqueira, Portugal has produced fine, light brown crystals, some transparent. Minas Gerais, Brazil, has also yielded large and fine crystals.
Other notable gem-quality sources include:
- Mt. Ste. Hilaire, Quebec, Canada: brown rhombs up to 15 inches on edge.
- Ivigtut, Greenland: rich brown, gemmy-looking crystals in cryolite.
- Cornwall, England: greenish crystals, some transparent (chalybite).
- United States: Colorado; Connecticut; Idaho.
- Austria; France; Germany; Italy.
Rare faceted pieces usually range in size from 1-5 carats.
- National Museums of Canada (Ottawa, Ontario): 2.60. 2.25 (light brown, Quebec, Canada).
You’re more likely to encounter siderites in gem collections than in jewelry collections. Store them separately from other stones to avoid contact scratches. Consult our gemstone jewelry cleaning guide for more recommendations.