Formula: CaBe(PO₄)(OH)

Species:

Colour: Colorless, gray, brown, pale yellow, greenish white, light blue, purple; colourless in transmitted light.

Lustre: Sub-Vitreous, Resinous, Waxy, Greasy

Hardness: 5 – 5½

Specific Gravity: 2.95

Crystal System: Monoclinic

Member of: Herderite Subgroup > Herderite Group > Gadolinite Supergroup

Name: Named “hydro-herderite” in 1894 by Samuel L. Penfield. Named changed to “hydroxyl-herderite” by Palache, Berman, and Frondel in 1954. The root name refers to Siegmund August Wolfgang von Herder (1776-1838), mining official in Freiberg, Germany. The “hydroxyl-” prefix signifies the dominance of hydroxide over fluorine.

Hydroxylherderite is isotypic with Datolite. Found usually as a pegmatite mineral formed during late stage hydrothermal deposition.