Håleniusite-(La), (La, Ce)OF is a yellow isometric mineral. It has a dull, earthy luster. It was discovered in 1986 at Bastnäs mines, Riddarhyttan, Skinnskatteberg, Västmanland, Sweden and named in honor of Ulf Hålenius, director of the mineralogy department at the Swedish Museum of Natural History in Stockholm, Sweden.
- Formula: (La, Ce)OF
- Specific Gravity: 6.5
- Crystal System: Isometric
- Name: Named in 2004 by Dan Holtstam, Jekabs Grins, and Per Nysten in honor of Prof. Ulf Hålenius (b. 1951).
- Lustre: Dull, Earthy
- Colour: lemon yellow to ochre yellow
- Streak: light yellow
- Density :6.5 g/cm3 (Measured)
- Cleavage: Unknown, Unknown, Unknown
- Diaphaneity: Translucent
Occurrence: Formed by alteration of primary bastnäsite-(La), most likely by a decarbonation reaction. The geological setting of håleniusite-(La) is in vugs and leaching zones of massive ferriallanite-(Ce), intimately intergrown with cerite-(Ce) and bastnäsite-(La).
Association: Ferriallanite-(Ce), bastnåsite-(La), quartz.