Behoite

gadolinite

tengerite

Formula: Be(OH)2
Hydroxide, dimorph of clinobehoite
Specific gravity: 1.92
Hardness: 4
Streak: White
Colour: Colourless or white, rarely pale pink to pale grey; may show anomalous blue and brown interference colours in transmitted light
Environments

Pegmatites

Behoite occurs in granite pegmatites and altered volcanic tuff (Webmin)

Localities

At Mont St-Hilaire, Quebec, Canada, behoite occurs in pegmatite veins and miarolitic cavities in nepheline syenite (HOM), and as coatings on serandite (Dana).

At Sierra Blanca, Hudspeth county, Texas, USA, behoite occurs with bertrandite and fluorite (Dana).

At the type locality, the Rode Ranch pegmatite, Llano county, Texas, USA, behoite occurs in a granite pegmatite as a near-surface alteration product of gadolinite (Mindat, HOM, Webmin). The Rode Ranch pegmatite contains the primary minerals allanite, gadolinite, zircon variety crytolite and fergusonite in a matrix of albitic plagioclase and microcline. The behoite crystals and aggregates occur in altered zones or rinds around masses of gadolinite. The alteration zone contains a mixture of several minerals, including bastnäsite, tengerite, nontronite and hematite, and behoite as euhedral crystals hosted by some of the hematite. It seems that the rarity of behoite is a result of the dispersal and low abundance of beryllium in rocks, and the great stability of most beryllium minerals, such as beryl, chrysoberyl and phenakite, in surface weathering. In those rare occurrences of unstable beryllium-bearing minerals in the weathering zone, such as epididymite and gadolinite, behoite may form (AM 55.1-9).
Associated minerals at the type locality include gadolinite, bastnäsite, tengerite, quartz, albite, microcline, montmorillonite, fluorite and calcite (HOM, Mindat, Dana).

At Honeycomb Hills, Utah, USA, behoite occurs in altered volcanic tuff (HOM).

Alteration

bromellite and H2O to behoite
BeO + H2O ⇌ Be(OH)2
Decreasing temperature favours the forward reaction, which occurs in the 200oC range (AM 71.277-300).

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