Bastnäsite

Bastnasite (also spelled bastnäsite or bastnaesite) is a rare earth fluorocarbonate mineral rich in the light rare earths, above all cerium. The U.S. Geological Survey says it "may be considered the most important REE mineral" because it is the primary ore mineral at Mountain Pass in California and Bayan Obo in China, the world's two largest rare earth deposits (USGS Professional Paper 1802-O).

What bastnasite is

Bastnäsite is a group of minerals with the general formula (REE)(CO₃)F: a rare earth carbonate that also carries fluorine (USGS). The common species is the cerium-dominant bastnäsite-(Ce), Ce(CO₃)F. It is named after its type locality, the Bastnäs Mine in the Riddarhyttan district of Västmanland, Sweden, and has been a recognized species since 1841 (Webmineral).

Bastnäsite-(La), La(CO₃)F, was approved in 1966, with its type locality in the Gallinas Mountains of New Mexico (Webmineral). Bastnäsite-(Y), Y(CO₃)F, was approved in 1970, with its type locality in Kazakhstan (Webmineral).

Bastnäsite-(Ce) forms hexagonal crystals, yellow to reddish brown with a vitreous to greasy luster. It has a hardness of 4 to 5 and a density of 4.95 to 5 (Webmineral).

What's in bastnäsite: cerium, lanthanum and neodymium

The mineral contains about 70% rare earth oxide, mostly light rare earths, according to a 1998 USGS report (USGS OFR 98-125). Cerium typically makes up almost half of the contained rare earths, and lanthanum and neodymium account for most of the rest.

The same USGS report says bastnäsite commonly contains less than 1% heavy rare earths, so it cannot supply them to industry. USGS contrasts bastnäsite ores with China's ion-adsorption clays, which are valued for their medium and heavy rare earth content (USGS PP 1802-O).

Where bastnäsite is found

Bastnäsite is typically the most significant rare earth source in carbonatite deposits, and carbonatites have been the world's main source of light rare earths since the 1960s (USGS PP 1802-O). Parisite, synchysite, ancylite and monazite occur with it. USGS names these deposits:

• Mountain Pass, California. The Sulphide Queen carbonatite holds about 10% to 15% bastnäsite plus lesser parisite. It is the only known carbonatite where the ore minerals are interpreted to have crystallized directly from magma. Elsewhere bastnäsite is interpreted to have formed later, from hydrothermal fluids, often as fine-grained fibrous or platy masses with quartz, fluorite, strontianite, barite and hematite.
• Bayan Obo, China. Baotou Rare Earth's mine produces iron ore along with bastnäsite and monazite as its main rare earth minerals.
• Bear Lodge, Wyoming. The altered, oxidized upper zones carry bastnäsite-group minerals, cerianite and local monazite.
• Maoniuping, Daluxiang and Weishan, China. Three more carbonatite deposits on the USGS list.

Other projects tied to the mineral:

• Ngualla, Tanzania. The project is hosted in the Ngualla Carbonatite. A 2016 project profile said development would target the weathered Bastnaesite Zone (Mining Technology). Ngualla's rare earths sit mainly in bastnäsite and synchysite, with comparatively low thorium and uranium (REEx).
• Nechalacho, Northwest Territories, Canada. In 2021 Vital Metals described it as a high-grade bastnäsite project (Vital Metals).
• Wigu Hill, Tanzania. In the same 2021 report, Vital Metals described it as a large carbonatite with bastnäsite mineralization (Vital Metals).
• Dong Pao, Vietnam. The ore carries bastnäsite with barite, quartz and fluorite (Ito, CIM 2013).
• Gakara, Burundi. Rainbow Rare Earths reports extensive veins of nearly pure bastnäsite and monazite (Rainbow Rare Earths).

How bastnäsite ore is processed

At Mountain Pass, MP Materials mines primarily bastnäsite ore and processes it in five steps: mining and crushing, milling and froth flotation, roasting with leaching and impurity removal, separation and extraction, and product finishing (MP Materials 10-K, February 2026).

An oxidizing roast turns the cerium in the concentrate into tetravalent cerium, which barely dissolves in the leach. The most abundant rare earth drops out early, without selective extraction. Roasting also allows a lower-temperature leach, which MP says cuts maintenance costs and downtime (MP 10-K). The carbonate in the mineral is released as carbon dioxide during processing (USGS).

Bastnäsite ore commonly comes with fluorite, barite and quartz, and flotation has to separate the rare earth mineral from them. REEx has covered a review proposing how to design reagents that separate bastnäsite from fluorite, with no tested results yet. A laboratory study of upgrading bastnäsite ore from Vietnam's Dong Pao deposit, limited to that single ore body, found that moderate reagent doses at near-neutral pH beat heavier dosing.

Bastnasite vs monazite

Monazite is a rare earth phosphate. One clear difference is thorium and uranium content, which makes monazite more radioactive. Bastnäsite reportedly carries 0% to 0.3% thorium dioxide and about 0.09% uranium dioxide, while monazite can carry up to 20% thorium dioxide and up to 16% uranium dioxide (USGS PP 1802-O).

The chemistry used to break them down also differs. Carbonate minerals such as bastnäsite can be decomposed with either acids or alkalis, while phosphate minerals like monazite are treated mainly with alkalis or sulfuric acid (Edwards, CIM 2012).

Who mines bastnäsite (as of February 2026)

In 2025 bastnäsite was mined as a primary product at Mountain Pass, and U.S. output of rare earth mineral concentrates, excluding monazite, was an estimated 51,000 metric tons of rare earth oxide, according to the USGS Mineral Commodity Summaries 2026. Rare earth mining at Mountain Pass began in 1952 under Molybdenum Corporation of America. Its operator today, MP Materials, describes itself as the largest producer of rare earth materials in the Western Hemisphere (MP 10-K). REEx has called bastnäsite the backbone of U.S. rare earth production.

Rainbow Rare Earths' Gakara project in Burundi was on care and maintenance at the government's request in 2025 (Rainbow Rare Earths).

Frequently asked questions