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.[1]

Herderite
Herderite-gem7-08a.jpg
General
CategoryPhosphate mineral
Formula
(repeating unit)
CaBe(PO4)(F,OH)
Strunz classification8.BA.10
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Unit cella = 4.81, b = 7.7,
c = 9.82 [Å]; β = 90.1°; Z = 4
Identification
ColourColourless, pale yellow, greenish-white
Crystal habitOccurs as prismatic tabular crystals, pseudo-orthorhombic or pseudo-hexagonal; fibrous botryoidal to spheroidal aggregates
TwinningOn {100} or {001} as fishtail contact
CleavageIndistinct on {110}
FractureSubconchoidal
Mohs scale hardness5 - 5.5
LustreVitreous
DiaphaneityTransparent - translucent
Specific gravity3.02
Optical propertiesBiaxial (-)
Refractive indexnα = 1.556 - 1.592 nβ = 1.578 - 1.610 nγ = 1.589 - 1.620
Birefringenceδ = 0.033
2V angleCalculated: 70°
Ultraviolet fluorescenceFluoresces violet under UV; cathodoluminesces and phosphoresces pinkish orange under X-rays
References[1][2][3]

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, Erzgebirge, Saxony, Germany. It was named for Saxon mining official Sigmund August Wolfgang von Herder (1776–1838).[1]

ReferencesEdit