bast·naes·ite or bast·näs·ite also bast·nas·ite 
(băstnə-sīt′)
(băstnə-sīt′)n.
A yellowish to reddish-brown mineral, (Ce,La, Y)CO3F, that is a source of several rare-earth elements including gadolinium, samarium, and neodymium.
[After Bastnäs, a mine in south-central Sweden.]