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Formula: Na3Mg(PO4)(CO3)
Phosphate-carbonate
Crystal System: Monoclinic
Specific gravity: 2.734 measured, 2.72 calculated
Hardness: 3 to 4
Streak: White
Colour: Light grey
Solubility: Slowly decomposed by cold water with Na2CO3 released to solution, readily soluble in
dilute hydrochloric acid
Environments:
Plutonic igneous environments
Carbonatites
Sedimentary environments
Bradleyite is a rare mineral in oil shale deposits of the Green River formation in Colorado, Wyoming and Utah,
USA, where it is associated with shortite,
clay minerals, trona,
pirssonite, northupite,
gaylussite and alstonite. It may
occur as fluid inclusions in chromite and has been found as inclusions in
diamond
(AM 110.12.2017-2028, HOM).
Bradleyite is a polygenetic mineral. In continental salt deposits, it forms under atmospheric pressure
sedimentation. In deep-formed igneous rocks, such as kimberlites and
carbonatites, bradleyite occurs as a product of
late-stage crystallisation of carbonatitic melt and as a
primary-crystallised phase in deep-seated minerals, such as
olivine, ilmenite,
chrome spinel and magnetite
(AM 110.12.2017-2028).
Localities
At the Sorriso river, Juína, Mato Grosso, Brazil, a bradleyite sample was found as an inclusion in a
diamond from the placer deposit. Bradleyite is part of a polymineral
inclusion, comprising a porous aggregate of grains less than 150 nm in size, hosted within a
dolomite crystal. Findings
demonstrate its stability in diamond and
diamond-forming environments and it may be considered a product of
crystallisation from a primary melt inclusion
(AM 110.12.2017-2028).
At the type locality, the John Hay Jr. Well No. 1, Sweetwater County, Wyoming, USA, bradleyite has been found in
the oil shale of the drill core from which
shortite was obtained. Bradleyite was found as a layer an inch thick at
a depth of 4036 m. Other saline minerals in the drill core include trona,
shortite, pirssonite,
gaylussite, alstonite and
northupite. Montmorillonite,
quartz, dolomite and
pyrite are also present.
The one-inch layer of very fine grained bradleyite contains about 30 per cent of much coarser
shortite, and 10 per cent of clay
(montmorillonite). The clay
contains organic matter which yields oil when heated in a closed tube. The crystals of
shortite have been partly replaced by bradleyite. Above the
bradleyite, the core consists essentially of shortite and
northupite with a little clay;
below the bradleyite, it consists of brown clay which contains about
40 per cent of shortite and 20 per cent of
northupite. In both parts of the core the
northupite is later than the
shortite.
The bradleyite is extremely fine grained. Hardly any grain is more than 0.002 mm across. The light-grey colour
of the sample is probably due to admixed darker clay.
(AM 26.646-650)
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