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Formula: Ca2CaUO6
Oxide, vapnikite subgroup,
perovskite supergroup,
uranium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 5.322 calculated for the empirical formula
Hardness: 5
Streak: White with a yellow hue
Colour: Yellow-brown
Luminescence: Sometimes weak yellowish fluorescence under UV
Solubility: Insoluble in 10% hydrochloric acid
RADIOACTIVE
Environments
Vapnikite is a relatively new mineral, approved in 2013. In the Hatrurim Formation it is formed by
pyrometamorphism due to combustion of organic-rich material at temperatures above 800 °C, during a retrograde stage by
fluids/melts of high alkalinity. Associated minerals include larnite,
brownmillerite, ye’elimite,
vorlanite and
fluorellestadite
(HOM).
Localities
At the type locality, Jebel Harmun, Quds Governorate, West Bank, Palestine, numerous tiny vapnikite grains,
less than 10 microns in size, were discovered in larnite-rich pyrometamorphic
pseudoconglomerates of the Hatrurim Formation.
Larnite rocks were formed by pyrogenic metamorphism due to caustobiolith (a
rock with a fairly high content of organic carbon compounds) combustion at temperatures above 800oC. Their
pebble-like shape can be explained by low-temperature hydrothermal alteration of
larnite-rich rocks with subsequent
weathering. The Jabel Harmun is also the locality where harmunite,
nabimusaite and fluormayenite
were discovered.
Only one dark-brown larnite pebble contained xenomorphic grains of
vapnikite up to 30 microns in size. The dark brown colour of the pebble is due to abundant grains of
brownmillerite. Other rock-forming minerals present include
ye’elimite and/or minerals of the
fluormayenite-fluorkyuygenite
series.
Some rock fragments are enriched in
fluorellestadite–fluorapatite,
phosphorus-bearing ternesite,
shulamitite, baryte,
periclase and barium-bearing
nabimusaite. Rarely, these rocks contain
oldhamite. In pebbles, vapnikite is often associated with
vorlanite.
Vapnikite is transparent with a strong vitreous lustre
(MM 78.3.571-581).
Vapnikite from Jebel Harmun - Image
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