Brockite

(repeating unit)(Ca,Th,Ce)PO₄·H₂OIMA symbolBck^[1]Strunz classification8.CJ.45Crystal systemHexagonalCrystal classTrapezohedral (622)
H-M symbol: (622)Space groupP6₂22 or P6₄22Unit cella = 6.98 Å, c = 6.40 Å; Z = 3IdentificationColorReddish brown, yellow (red brown due to inclusions of hematite)Crystal habitRarely as Stubby hexagonal prisms rare; common as granular massive aggregates, cryptocrystallineCleavageNone observedFractureConchoidalTenacityBrittleMohs scale hardness3 - 4LusterGreasy to vitreousDiaphaneityTranslucent to opaqueSpecific gravity3.9 (measured)Optical propertiesUniaxial (+)Refractive indexn_ω = 1.680 n_ε = 1.695Birefringenceδ = 0.015Other characteristicsRadioactiveReferences^[2][3][4]

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

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]

References