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Formula: Be(OH)2
Hydroxide, paramorph of
clinobehoite
Crystal System: Orthorhombic
Specific gravity: 1.92 measured, 1.93 calculated
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
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 the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, behoite was found in a partially filled mould
where beryl had decomposed. The void contained tiny loose crystals of
bertrandite and behoite as masses and crystals to 1 mm. The Emmons
pegmatite is an example of a highly evolved
boron - lithium -
cesium - tantalum
enriched pegmatite
(R&M 94.6.503).
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, cyrtolite 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-(Y), 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-(Y),
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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