Herderite

(repeating unit)CaBe(PO₄)(F,OH)IMA symbolHrd^[1]Strunz classification8.BA.10Crystal systemMonoclinicCrystal classPrismatic (2/m)
(same H-M symbol)Space groupP2₁/aUnit cella = 4.81, b = 7.7,
c = 9.82 [Å]; β = 90.1°; Z = 4IdentificationColourColourless, pale yellow, greenish-whiteCrystal habitOccurs as prismatic tabular crystals, pseudo-orthorhombic or pseudo-hexagonal; fibrous botryoidal to spheroidal aggregatesTwinningOn {100} or {001} as fishtail contactCleavageIndistinct on {110}FractureSubconchoidalMohs scale hardness5 - 5.5LustreVitreousDiaphaneityTransparent - translucentSpecific gravity3.02Optical propertiesBiaxial (-)Refractive indexn_α = 1.556 - 1.592 n_β = 1.578 - 1.610 n_γ = 1.589 - 1.620Birefringenceδ = 0.0332V angleCalculated: 70°Ultraviolet fluorescenceFluoresces violet under UV; cathodoluminesces and phosphoresces pinkish orange under X-raysReferences^[2][3][4]

Herderite is a phosphate mineral belonging to the apatite, phosphate group, with formula CaBe(PO₄)(F,OH). It forms monoclinic crystals, often twinned and variable in colour from colourless through yellow to green. It forms a series with the more common hydroxylherderite, which has more hydroxyl ion than fluoride.^[2]

It is found in many parts of the world, often in pegmatites and associated with other apatite minerals.

It was first described in 1828 for an occurrence in the Sauberg Mine, Ore Mountains, Saxony, Germany. It was named for Saxon mining official Sigmund August Wolfgang von Herder (1776–1838).^[2]

References