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Formula:(K,Na)(UO2)(SiO3OH).1.5H2O
Nesosilicate (insular SiO4 groups), uranyl mineral,
uranophane group
Crystal System: Monoclinic
Specific gravity: 4.7 measured, 4.46 calculated
Hardness: 3½ to 4
Streak: White
Colour: Pale yellow, orange yellow
Luminescence: Dull green in both short and long wave UV
Common impurities: Fe,Ca,Na
RADIOACTIVE
Environments
Plutonic igneous environments
Pegmatites
Sedimentary environments
Boltwoodite typically occurs as clusters of radiating acicular to fibrous crystals with individual crystals to
2cm, but usually smaller. Also as poorly crystallised earthy masses at some localities (R&M 96.3.238-245).
Boltwoodite is found in the outer silicate zone of alteration surrounding hydrated uranyl oxides incrusting
primary uraninite;
also filling fractures at some distance from primary
uraninite. From
pegmatite and Colorado-Plateau-type
sandstone uranium deposits. Associated minerals include
uraninite, becquerelite,
fourmarierite,
phosphuranylite, gypsum and
fluorite
(HOM).
Localities
At Arandis, Arandis Constituency, Erongo Region, Namibia, boltwoodite occurs in radial aggregates up to 2 cm long
(Dana).
At Goanikontes, Goanikontes, Arandis Constituency, Erongo Region, Namibia, spectacular specimens of bright orange
sprays of boltwoodite to 7 mm occur on light coloured and dark calcite.
The boltwoodite is found in light-coloured granite that hosts
both primary and
secondary uranium mineralisation. It consists of bright yellow
to orange prismatic crystals to 2 cm that fluoresce reddish orange in long wave UV, but show no response under short wave.
Most of the specimens are on a matrix of masses of small scalenohedral crystals of
calcite, frequently coated by dark iron or manganese oxides. These oxides
include cryptomelane, goethite,
ranciéite, pyrolusite
and uraninite, and
they are also found as inclusions in the calcite. Later overgrowths of
gypsum on the boltwoodite are common.
(R&M 96.3.238-245).
Boltwoodite from Goanikontes - Image
At the New Method Mine, Amboy area, Bristol Mountains, San Bernardino county, California, USA, small free-standing
sprays of lemon-yellow crystals of boltwoodite occur, some of which are associated with small
calcite crystals and perfect cubes of dark purple mm sized
fluorite
(R&M 96.3.238-245).
Boltwoodite from the New Method Mine - Image
At the Sherrer Quarry, C.K. Williams Quarry complex, Chestnut Hill, Easton, Northampton county, Pennsylvania, USA,
boltwoodite occurs as an alteration of thorian uraninite
(Dana).
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At the type locality, Pick's Mine, Delta, San Rafael Mining District, Emery county, Utah, USA, boltwoodite occurs
as wart-like aggregates of fibres coating fractures in sandstone. It is
an oxidation product of primary black uranium ores
(AM 42.307-308). Associated minerals include becquerelite,
brochantite, fluorite,
fourmarierite, gypsum,
phosphuranylite, uraninite,
pyrite, tyuyamunite and
zippeite
(R&M 96.3.238-245).
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