Siderite Value, Price, and Jewelry Information

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Brown siderite, 1.66 cts, 7.6 x 7.5 x 4.2 mm, 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 Information

Data Value
Name Siderite
Crystallography Hexagonal (R) (trigonal). Crystals rhomb shaped; also massive, granular; globular; oolitic.
Crystallographic Forms
Refractive Index 1.633-1.873
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.
Hardness 3.5-4.5
Fracture Conchoidal to uneven
Specific Gravity 3.83-3.96
Birefringence 0.240
Cleavage Perfect rhombohedral
Luminescence None
Luminescence Present No
Transparency Transparent to opaque
Absorption Spectrum Not diagnostic
Formula FeCO3
Optics o = 1.873; e = 1.633. Uniaxial (-).
Optic Sign 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.
siderites - 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. 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, Used with permission.

What is Siderite?

Siderite forms three solid-state 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.

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

A fan-shaped bladed crystal of siderite 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, Used with permission.

Does Siderite Make a Good Jewelry Stone?

Rhodochrosite, smithsonite, and magnesite 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).

You’re more likely to find siderites on display in mineral and gem collections than worn as jewelry pieces. They’re difficult to cut and too soft for ring use without protective settings. They would be best reserved for occasional wear. Use for earrings, pendants, and brooches would be more advisable.

Nevertheless, as faceted pieces, these golden and honey-colored gems would make unusual, prized additions to show off in any gem collection. In particular, Portuguese rough has yielded beautiful faceted stones.

Are There Synthetic Siderites?

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.

Siderites usually receive no treatments or enhancements.

Where are Siderites Found?

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 the following:

  • 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

Faceted siderite, Morro Velho mine, Nova Lima, Minas Gerais, Southeast Region, Brazil, 5 x 3.2 mm. Photo by Didier Descouens. Licensed under CC By-SA 3.0.

Siderite Sizes

Rare faceted pieces usually range in size from 1 to 5 carats.

  • National Museums of Canada (Ottawa, Ontario): 2.60. 2.25 (light brown, Quebec, Canada).

How to Care for Siderites

Store siderites separately from other stones to avoid contact scratches. Avoid cleaning these gems with mechanical cleaning systems, like steam and ultrasound. Clean them only with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more recommendations.

Siderite - Portugal

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

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