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Microphoto of brockite on thorite (black).
Field view: 2 x 2 mm.
CategoryPhosphate mineral
(repeating unit)
IMA symbolBck[1]
Strunz classification8.CJ.45
Crystal systemHexagonal
Crystal classTrapezohedral (622)
H-M symbol: (622)
Space groupP6222 or P6422
Unit cella = 6.98 Å, c = 6.40 Å; Z = 3
ColorReddish brown, yellow (red brown due to inclusions of hematite)
Crystal habitRarely as Stubby hexagonal prisms rare; common as granular massive aggregates, cryptocrystalline
CleavageNone observed
Mohs scale hardness3 - 4
LusterGreasy to vitreous
DiaphaneityTranslucent to opaque
Specific gravity3.9 (measured)
Optical propertiesUniaxial (+)
Refractive indexnω = 1.680 nε = 1.695
Birefringenceδ = 0.015
Other characteristicsRadioactive

Brockite is a rare earth phosphate mineral with formula: (Ca,Th,Ce)PO4·H2O. It crystallizes in the hexagonal system in the chiral space group 180 or its enantiomorph 181. It is typically granular to massive with only rare occurrence of stubby crystals. It is radioactive due to the thorium content.

Discovery and occurrence[edit]

Brockite was first described in 1962 for an occurrence in the Bassick Mine area, Querida, Wet Mountains, Custer County, Colorado, US. It was named for Maurice R. Brock, of the U.S. Geological Survey.[3]

Brockite occurs in granite and granite pegmatite as an accessory mineral. Associated minerals include monazite, bastnasite, xenotime, thorite, zircon, apatite, rutile and hematite.[2]


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Brockite in the Handbook of Mineralogy
  3. ^ a b Brockite on
  4. ^ Brockite data on Webmineral