Brockite

Microphoto of brockite on thorite (black).
Field view: 2 x 2 mm.

General
Category| Phosphate mineral
Formula
(repeating unit)| (Ca,Th,Ce)PO4·H2O
Strunz classification| 8.CJ.45
Crystal system| Hexagonal
Crystal class| Trapezohedral (622)
H-M symbol: (622)
Space group| P6222 or P6422
Unit cell| a = 6.98 Å, c = 6.40 Å; Z = 3
Identification
Color| Reddish brown, yellow (red brown due to inclusions of hematite)
Crystal habit| Rarely as Stubby hexagonal prisms rare; common as granular massive aggregates, cryptocrystalline
Cleavage| None observed
Fracture| Conchoidal
Tenacity| Brittle
Mohs scale hardness| 3 - 4
|re|er}}| Greasy to vitreous
Diaphaneity| Translucent to opaque
Specific gravity| 3.9 (measured)
Optical properties| Uniaxial (+)
Refractive index| nω = 1.680 nε = 1.695
Birefringence| δ = 0.015
Other characteristics| Radioactive
References| [1][2][3]

Brockite is a rare earth phosphate mineral with formula: (Ca,Th,Ce)PO
4·H
2O. 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.[2]

Brockite occurs in granite and granite pegmatite as an accessory mineral. Associated minerals include monazite, bastnasite, xenotime, thorite, zircon, apatite, rutile and hematite.[1]

## References

1. ↑ 1.0 1.1 Brockite in the Handbook of Mineralogy
2. ↑ 2.0 2.1 Brockite on Mindat.org
3. ↑ Brockite data on Webmineral
4. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.

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