Sodium iron amphibole. Fibrous variety is crocidolite blue asbestos ; non-fibrous form found in alkaline igneous rocks. Color: Dark blue to black. Luster: Vitreous to silky. Streak: Blue-gray. Cleavage: Good in two directions at 56°. Hardness: 5-6. Transparency: Translucent to opaque. Crystal system: Monoclinic. Chemical formula: Na₂Fe₃²⁺Fe₂³⁺Si₈O₂₂ OH ₂. Specific gravity: 3.0-3.4. Formation: Forms in sodium-rich, silica-poor igneous rocks and in iron-rich metamorphic rocks. Common geological settings: South Africa, Australia, Bolivia, USA; crocidolite historically mined as blue asbestos. Common look-alikes and related entries: Glaucophane, Hornblende, Arfvedsonite. Specimen safety: Some fibrous habits or varieties in this mineral group may be asbestos. Treat any fibrous specimen as suspect: do not disturb, break, brush, cut, grind, or clean it. Isolate it in a closed, clearly labelled container and seek qualified local guidance.
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These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.
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Last updated
2026-03-30T14:38:05.588374+00:00
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Published; not independently peer-reviewed
IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.
Asbestos fact sheet — U.S. Occupational Safety and Health Administration. Official guidance on asbestos fibre release, health risks, exposure prevention, and respiratory protection.
Sodium iron amphibole. Fibrous variety is crocidolite blue asbestos ; non-fibrous form found in alkaline igneous rocks.
How can you identify Riebeckite?
Compare several properties rather than relying on colour alone. This entry records colour: Dark blue to black; lustre: Vitreous to silky; streak: Blue-gray; Mohs hardness: 5-6; cleavage: Good in two directions at 56°; crystal system: Monoclinic; transparency: Translucent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.
How does Riebeckite form?
Forms in sodium-rich, silica-poor igneous rocks and in iron-rich metamorphic rocks.
Where is Riebeckite commonly found?
South Africa, Australia, Bolivia, USA; crocidolite historically mined as blue asbestos.
Is Riebeckite safe to handle?
Some fibrous habits or varieties in this mineral group may be asbestos. Treat any fibrous specimen as suspect: do not disturb, break, brush, cut, grind, or clean it. Isolate it in a closed, clearly labelled container and seek qualified local guidance. Avoid creating dust or using destructive tests on an unknown specimen, and follow site-specific safety procedures.
What is Riebeckite commonly confused with?
Riebeckite may be confused with Glaucophane, Hornblende, Arfvedsonite. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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