Riebeckite

Crocidolite from Wittenoom, Western Australia

Riebeckite is a sodium-rich member of the amphibole group of minerals, chemical formula Na₂(Fe,Mg)₅Si₈O₂₂(OH)₂. It crystallizes in the monoclinic system, usually as long prismatic crystals showing a diamond-shaped cross section, but also in fibrous, bladed, acicular, columnar, and radiating forms. Its Mohs hardness is 5.0–6.0, and its specific gravity is 3.0–3.4. Cleavage is perfect, two directions in the shape of a diamond; fracture is uneven, splintery. It is often translucent to nearly opaque. It was named after German explorer Emil Riebeck (1853-1885).

It typically forms dark-blue elongated to fibrous crystals in highly sodic granites, syenites, iron formations and schists.

Some forms of riebeckite are asbestiform, notably crocidolite, also known as blue asbestos.

Riebeckite granite

The riebeckite granite known as ailsite, found on the island of Ailsa Craig in western Scotland, is prized for its use in the manufacture of curling stones.

Canton viaduct

Riebeckite granite was used for the facing stones of the Canton Viaduct from Moyles Quarry (a.k.a. Canton Viaduct Quarry) now part of Borderland State Park in Massachusetts.

See also

• List of minerals
• List of minerals named after people

References

• Webmineral.com

External links

Wikimedia Commons has media related to: Riebeckite

•  "Crocidolite". Encyclopædia Britannica (11th ed.). 1911.