Riebeckite
From Wikipedia, the free encyclopedia
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.
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[edit] 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.
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.
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[edit] External links
"Crocidolite". Encyclopædia Britannica (11th ed.). 1911.
