Siderite Value, Price, and Jewelry Information


Brazilian siderite - faceted
“Siderite,” 1.66-ct, 7.6 x 7.5 x 4.2 mm, brown, Brazil. © ARK Rare Gems. Used with permission.

Siderite is difficult to cut, but this light brown collector's gem has yielded faceted pieces of great beauty.

Siderite Value

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Siderite Information

DataValue
NameSiderite
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 Brittle.
Hardness 3.5-4.5.
Specific Gravity 3.83-3.96.
Birefringence 0.240.
Cleavage Perfect rhombohedral.
Luminescence None.
Spectral Not diagnostic.
Transparency Transparent to opaque.
FormulaFeCO3.
Optics o = 1.873; e = 1.633. Uniaxial (-).
EtymologyFrom the Greek sideros for “iron,” in reference to its composition.
OccurrenceA widespread mineral in sedimentary deposits; hydrothermal ore veins; also in pegmatites; basaltic rocks.
siderite - rough and cut set
This siderite and blue-green apatite rough specimen comes from Linopolis, Minas Gerais, Brazil. The golden siderite gem, a modified brilliant cut-corner rectangle, comes from Bolivia. “Siderite (Rough and Cut Set),” 4.3 x 3.8 x 2.3 cm (specimen); 8.07 mm x 6.43 mm, 2 cts (gem). © Rob Lavinsky, www.iRocks.com. Used with permission.

Comments

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.

siderite - Portuguese crystal
“Siderite,” a fan-shaped bladed crystal with an inter-grown quartz crystal, lower right. 4.6 x 4.0 x 2.5 cm, Panasqueira Mine – Couto Mineiro da Panasqueira, Panasqueira, Covilha, Castelo Branco District, Portugal. © Rob Lavinsky, www.iRocks.com. Used with permission.

Synthetics

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.

Enhancements

None known.

Sources

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.
siderite - faceted gem, Brazil
“Cut Siderite,” Morro Velho mine, Nova Lima, Minas Gerais, Southeast Region, Brazil, 5 x 3.2 mm, by Didier Descouens. Licensed under CC By-SA 3.0.

Stone Sizes

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).

Care

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.

siderite - Portugal
Siderite: Portugal (1.40). Photo © Joel E. Arem, PhD, FGA. Used with permission.