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Formula: Ca5(SiO4)1.5(SO4)1.5OH
Nesosilicate (insular SiO4 groups), ellestadite group,
apatite supergroup, forms a series with
fluorellestadite and with
hydroxylapatite
Crystal System: Hexagonal
Specific gravity: 3.068 measured, 3.046 calculated
Hardness: 4½
Streak: White
Colour: Light orange, pink, purple-grey
Luminescence: Slightly fluorescent under UV (Cioclovina)
Common impurities: Al,Fe,Mn,Mg,Sr,Na,K,P,C
Environments
Pegmatites
Metamorphic environments
Hydroxylellestadite is found in pegmatite veins,
skarn and pyrometamorphic deposits
(Mindat).
Localities
At the type locality, the Chichibu mining district, Nakatsugawa, Ohtaki-mura, Chichibu City, Saitama Prefecture, Japan,
hydroxylellestadite was found among skarn minerals as a purplish
mass in association with diopside,
wollastonite,
clintonite, vesuvianite and
white calcite. Aluminum-deficient and sulphate-saturated conditions may promote
the formation of hydroxylellestadite instead of
scapolite which contains aluminium as well as sulphate. It should be noted
that no scapolite is found in the Chichibu mining area
(AM 56.1507-1518).
Minerals associated with hydroxylellestadite include
apatite, magnetite,
chlorite, tremolite and
calcite
(HOM).
Hydroxylellestadite from Chichibu - Image
At the Cioclovina cave, Boșorod, Hunedoara County, Romania, hydroxylellestadite is associated with
another high-temperature mineral, berlinite. It is likely to have formed
within highly phosphatised, silicate-rich, carbonate-mudstone sediments
heavily compacted and thermally transformed due to in situ bat guano combustion
(AM 91.1927-1931).
At the Crestmore quarries, Crestmore, Jurupa Valley, Riverside County, California, USA, hydroxylellestadite
occurs in contact metamorphosed
limestone, associated with
diopside, wollastonite,
vesuvianite, monticellite,
okenite and calcite
(HOM).
Hydroxylellestadite from Crestmore - Image
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