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Formula: Ca3[BO(OH)2]6.2H2O
Hydrated borate containing hydroxyl
Crystal System: Monoclinic
Specific gravity: 2.35 measured
Hardness: 3½
Streak: White
Colour: Colourless
Solubility: Insoluble in water, slowly soluble in 10% acetic acid or l0% hydrochloric acid at room temperature, dissolving
rapidly when warmed (AM 47.172).
Environments
Metamorphic environments
Hydrothermal environments
Nifontovite is an extremely rare borate
Localities
At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in
veins of hydrothermal origin in skarn. Nifontovite occurs as
colourless or cloudy white sheaves of elongated crystals reaching a length of 14 mm. Although nifontovite
specimens were found at the same time as olshanskyite and
pentahydroborite, specimens show no associations of nifontovite
with these other borate minerals
(R&M 96.5.402).
Charcas, San Luis Potosí, Mexico, is the locality for the finest nifontovite specimens in the world. Charcas is a
zinc-lead-silver-copper
skarn and high temperature carbonate replacement deposit
that formed in dacite and quartz
latite,
intruding limestone. Several hydrothermal stages at lower temperatures took
place and overprinted the earlier mineralisation.
Typical gangue minerals are danburite,
datolite, quartz and
calcite; less abundant are andradite
and vesuvianite. Principal metallic minerals include
pyrite, sphalerite,
galena, chalcopyrite,
tetrahedrite, pyrrhotite and small
amounts of silver sulphosalts.
Clear and transparent nifontovite crystals to 8 cm in length appear in cavities within the matrix, associated with
lizardite pseudomorphs after an
unknown precursor mineral, possibly periclase. Tiny grains of
andradite and vesuvianite represent
relict minerals and predate the low-temperature hydrothermal event responsible for the precipitation of nifontovite.
Three magnesium-rich minerals crystallised before nifontovite.
Clinochlore formed early, probably at the same time as
andradite, during
contact metamorphism. The second mineral is an unidentified mineral,
now pseudomorphed by lizardite.
It is most probably periclase, which typically forms from
dolomite or magnesite in a
contact metamorphic environment at high temperatures.
Lizardite usually forms at low temperatures, less than 100°C, and here it
replaced periclase? before or during the formation of nifontovite by
crystallisation of boron-rich, silica-poor low temperature epithermal solutions. There is no evidence of
danburite or datolite being precursor
minerals here
(R&M 85.2.165-169).
At the Fuka Okayama prefecture, Japan, nifontovite occurs in crystalline
limestone in the vicinity of
gehlenite-spurrite
skarn associated with quartz
monzonite dikes. Nifontovite formed by hydrothermal alteration of an
unknown anhydrous borate precurser. It occurs as aggregates to 5 cm long of tabular crystals, and rarely as euhedral crystals
to 1 mm (Minrec 36.4.375-376). Associated minerals include olshanskyite,
pentahydroborite, sibirskite
and calcite
(HOM).
At the type locality, the Novofrolovskoye boron-copper deposit, Tur'insk, Turya river, Turinsk-Auerbakovsk ore field,
Serovsky district, Sverdlovsk Oblast, Russia, nifontovite occurs in a skarn
formed by quartz diorite intruding
limestone 20-25 meters from the
pyroxene-garnet
skarn zone. Associated minerals include
andradite-grossular
garnet and szaibélyite; the latter occurs
as fine needles as inclusions in nifontovite
(AM 47.172, Minrec 36.4.375-376).
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