Minasgeraisite-(Y)

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Discredited in 2023

Formula: CaBe₂Y₂Si₂O₁₀
Nesosilicate (insular SiO₄ groups), gadolinite subgroup, gadolinite group, gadolinite supergroup, beryllium- and yttrium- bearing mineral
Crystal System: Triclinic
Specific gravity: 4.29 measured, 4.90 calculated for theoretically pure material
Hardness: 6 to 7
Streak: Very pale purple
Colour: Purple to lavender-purple
Luminescence: Not fluorescent under short wave or long wave UV
Magnetism: Not magnetic
Solubility: Soluble in acids
Environments

Pegmatites

Localities

At the type locality, the Jaguaraçu pegmatite, Jaguaraçu, Ipatinga, Minas Gerais, Brazil, minasgeraisite-(Y) occurs as a sparse, accessory, late-stage mineral in small druses in a zoned, complex, granitic pegmatite. The pegmatite has been mined for industrial beryl, and more recently for mineral specimens, mainly tourmalinated quartz crystals and cleavelandite druses. Most of the workings are underground, and the pegmatite is now abandoned and flooded. A replacement zone contains adularia, albite, hematite rosettes, muscovite, quartz and milarite. The largest milarites found were tan coloured, more than 30 mm in length, and implanted on druses of albite. Greenish-yellow and pale-tan milarite crystals were also found associated with druses of muscovite and tourmalinated quartz. Additional minerals present include amazonite, which has been replaced locally along cleavages by pink adularia, almandine-spessartine garnet crystals up to 1 cm across, magnetite in irregular masses up to 25 cm across, churchite-(Y), sky-blue elbaite in rare small irregular masses, pyrite in microscopic crystals, and nodules up to several centimetres across consisting of a mixture of cerussite and pyromorphite. Also present are numerous round and ocherous spots of light-yellow and powdery anatase.
Minasgeraisite-(Y) coats and is intergrown with the milarite, muscovite, quartz, albite, and rarely other minerals. The muscovite on which most of the minasgeraisite-(Y) occurs is a yellowish bronze coloured iron- and lithium- bearing variety. Minasgeraisite-(Y) occurs as single and multiple rosettes ranging from 0.2 mm to approximately 1.0 mm across. It was one of the latest minerals to form, and only quartz completely encloses it (AM 71.603-607).

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