Riebeckite

Description

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According to Wikipedia, Riebeckite, aka crocidolite, is “a sodium-rich member of the amphibole group of silicate minerals” and this one’s waiting to come home with you!

Riebeckite has a hardness of 5-6 and a specific gravity of 3-3.4, and 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. Cleavage is perfect, two directions in the shape of a diamond; fracture is uneven, splintery. It is often translucent to nearly opaque, and typically forms dark-blue elongated to fibrous crystals in highly alkali granites, syenites, granite pegmatites and schist. It occurs in banded iron formations as the asbestiform variety crocidolite (blue asbestos).

Riebeckite was first described in 1888 for an occurrence on Socotra Island, Aden Governorate, Yemen, and named after German explorer Emil Riebeck.

It occurs in association with aegirine, nepheline, albite, arfvedsonite in igneous rocks; with tremolite, ferro-actinolite in metamorphic rocks; and with grunerite, magnetite, hematite, stilpnomelane, ankerite, siderite, calcite, chalcedonic quartz in iron formations. It’s found in at least 8 counties in Colorado and over 1,000 locations worldwide.