Brockite: Properties and Occurrences

Brockite is a rare earth phosphate mineral with formula: (Ca, Th, Ce)PO4·H2O. It was named after Maurice R. Brock from the U.S. Geological Survey, who supplied the first specimen. It belongs to the rhabdophane group. It crystallizes in the hexagonal system. It is typically granular to massive with the only rare occurrence of stubby crystals. It is radioactive due to the thorium content.

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.

General Information

  • Category: Phosphate mineral
  • Formula: (Ca, Th, Ce)PO4·H2O
  • Crystal system: Hexagonal
  • Crystal class: Trapezohedral (622)


Brockite can be identified in the field by its color variations, such as white, light yellow, dark reddish-brown, and reddish-brown. Its translucent form has no cleavage. This mineral has a vitreous, greasy luster. The fracture of this mineral is conchoidal. The density of brockite is 3.7 – 4.1 g/cm3, with a hardness of 3 – 4 – between calcite and fluorite.

  • 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
  • Luster: Greasy to vitreous
  • Diaphaneity: Translucent to opaque
  • Specific gravity: 3.9 (measured)


Brockite occurs in a rare accessory mineral in granite and granite pegmatites. It is often associated with minerals such as monazite, bastnasite, apatite, xenotime, thorite, rutile, hematite, and zircon.

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


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