bastnäsite

Bastnäsite is a rare-earth bearing carbonate-fluoride mineral with a general chemical composition of (Ce,La,Nd,Y)CO3F. It belongs to the calcite group and crystallizes in the trigonal (rhombohedral) system. Bastnäsite forms as a primary mineral in carbonatites and pegmatites and occurs in hydrothermal veins. It is an important source of light rare earth elements (REEs), particularly cerium, lanthanum, and neodymium.

The mineral occurs in several varieties named for the dominant rare-earth element: bastnäsite-(Ce), bastnäsite-(La), bastnäsite-(Nd), and bastnäsite-(Y). Bastnäsite-(Ce) is the most common form. Substitution among REEs leads to solid solution across the different varieties.

In hand samples, bastnäsite ranges in color from colorless to pale yellow, pink, or brown, and it is typically transparent to translucent with a vitreous luster. It has a relatively high density, with specific gravity generally reported around 4.7 to 4.9. Crystals are commonly elongated and prismatic or occur as coarse aggregates. The streak is white, and the mineral may exhibit cleavage in certain directions consistent with its carbonate structure.

Bastnäsite is associated with other REE-bearing minerals such as monazite and xenotime, as well as fluorite and calcite in carbonatite complexes. It was named after Bastnäset, Sweden, the site of its first description in 1839.

Industrially, bastnäsite was historically a major ore of light REEs, providing access to elements used in modern electronics, magnets, and catalysts, though mining focus has shifted to broader REE deposits and processing routes.