Hydrated borate containing hydroxyl
Solubility: Insoluble in water, slowly soluble in 10% acetic acid or l0% hydrochloric acid at room temperature, dissolving rapidly when warmed (AM 47.172).
Nifontovite is an extremely rare borate
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 sulfosalts.
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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