Hydroxylherderite Locality: Virgem da Lapa , Jequitinhonha valley, Minas Gerais , Southeast Region, Brazil ( Locality at mindat.org ) Size: small cabinet, 9.7 x 7.2 x 3.1 cm Hydroxylherderite An approximately 2 x 2 x 1.5 cm sharp lavender-colored crystal, smartly perched as it were emerging from the matrix of feldspar. The crystal is 3-Dimensional, and complete all around, totally pristine. The matrix is actually a shard of a feldspar crystal, seemingly re-healed and complete-all-around. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Hydroxylherderite
The hydroxyl analogue of herderite — a calcium-beryllium phosphate of granitic pegmatites.
Intro adapted from Wikipedia (CC BY-SA).
Hydroxylherderite is an IMA-recognized mineral species in the phosphate class, with the chemical formula CaBe(PO₄)(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/a). It is a member of the Gadolinite structural group.
Key properties: Mohs hardness 5–5.5; specific gravity 2.95; Vitreous to subvitreous, resinous luster; optically biaxial.
IMA symbol Hhd, IMA status: approved, named in 1894.
A late-stage mineral in miarolitic cavities in complex granite pegmatites, of hydrothermal or probable pneumatolytic origin; can form from the alteration of beryl or beryllonite.
It is found associated with Elbaite, topaz, cassiterite, albite, microcline, muscovite, lepidolite, quartz.
The name refers to predominance of hydroxyl over fluorine in its composition and relation to herderite.