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Formula: Ba5(PO4)3Cl
Anhydrous phosphate containing halogen, apatite group,
apatite supergroup,
barium-bearing mineral
Crystal System: Hexagpnal
Specific gravity: 4.80 calculated
Hardness: 5
Streak: White
Colour: Colourless
Luminescence: Not fluorescent under UV, but intense violet cathodluminescence in 10 to 15 kV electron beam
Environments
Sedimentary environments
Metamorphic environments
Alforsite occurs in lenses and bands of barium silicate metasediments
developed under
hornblende-pyroxene
hornfels facies rocks near the contact with
granite or
granodiorite. Associated minerals include
celsian, witherite,
sanbornite, gillespite,
fresnoite, fluorapatite,
walstromite,
titantaramellite, quartz,
tourmaline and pyrite
(HOM).
Localities
There are two co-type localities, Big Creek and the Esquire No. 7 claim, Big Creek, both at the Big Creek-Rush Creek
Mining District, Fresno county, California, USA.
In the Big Creek-Rush Creek Mining District, Fresno county, California, USA, alforsite occurs as .05 mm or
smaller grains disseminated in fine-grained metamorphic
sanbornite-quartz rock. The
alforsite-bearing samples are massive grey rocks with gneissic
banding due primarily to segregations of quartz. The samples from Big Creek
which contain alforsite are lighter grey than those from Incline. They are
quartz-rich and contain no
gillespite. The alforsite and
fluorapatite are scattered within different fine-grained bands which
contain a high proportion of quartz and alternate with bands bearing
quartz in lesser amounts. Both bands contain abundant
celsian, witherite and
sanbornite with accessory, disseminated
fresnoite, walstromite,
tourmaline and pyrite. Nearly
pure fluorapatite is also common in these samples. The two
apatite group members
(fluorapatite
and alforsite) have not been found touching one another in thin section and are
generally in different bands in the rocks. Apatites typically form complete
solid solutions between end-members. Alforsite occurs in an assemblage of
sanbornite, quartz and
witherite
(AM 66.1050-1053).
At Incline, Clearing House Mining District, East Belt, Mariposa county, California, USA, alforsite occurs as
.05 mm or smaller grains disseminated in fine-grained metamorphic
sanbornite-quartz rock. The
alforsite-bearing samples are massive grey rocks with gneissic
banding due primarily to segregations of quartz. Prominent bands of pink
gillespite occur and here alforsite is
associated with sanbornite,
witherite and celsian in
quartz-rich and
gillespite-rich bands.
Fresnoite, walstromite,
tourmaline and pyrite, though
less abundant, are disseminated throughout the rock
(AM 66.1050-1053).
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