bastnasite

Bastnasite is a mineral group of rare-earth fluorocarbonates, with the general formula REECO3F, where REE stands for a rare-earth element. The best-known member is bastnäsite-(Ce), CeCO3F, with other end-members including bastnäsite-(La) LaCO3F, bastnäsite-(Nd) NdCO3F, and bastnäsite-(Pr) PrCO3F. In natural samples, compositions are often mixed, with cerium commonly dominant but other light rare-earth elements present.

Bastnasite crystallizes in the hexagonal system and occurs as prismatic to tabular crystals, often forming masses or lamellar aggregates. It is relatively soft and can be weathered to secondary minerals. The mineral is commonly altered in surface environments to form carbonates and fluorides of other elements.

Occurrence and formation: Bastnasite forms in carbonatite-related igneous complexes and associated hydrothermal systems. It is a principal ore mineral for light rare-earth elements, particularly cerium, lanthanum, and neodymium. It is frequently found together with fluorite, calcite, baryte, and other rare-earth minerals such as monazite and xenotime.

Economic significance: Bastnasite has been a major source of light rare-earth elements for industrial uses, especially when extracted from carbonatite-hosted ore deposits. The distribution and concentration of bastnasite influence the grade and extractive processing of rare earth elements.

Name and history: Bastnasite was first described from Bastnäset, Sweden, and the name is derived from that locality. The mineral has since been identified in carbonatite complexes around the world and remains a key ore mineral for light rare-earth elements.