COLUMBITE

columbite, a rare mineral consisting of iron niobate, fenb2o6, in which the iron and niobium are replaced by varying amounts of manganese and tantalum respectively, the general formula being (fe, mn) (nb, ta)2o6. it was in this mineral that charles hatchett discovered, in 1801, the element niobium, which he himself called columbium after the country (columbia or america) whence came the specimen in the british museum collection which he examined. the species has also been called niobite. it crystallizes in the orthorhombic system, and the black, opaque crystals are often very brilliant with a sub-metallic lustre. twinned crystals are not uncommon, and there is a distinct cleavage parallel to the face marked _b_ in the figure. hardness 6; specific gravity 5.3. with increasing amount of tantalum the specific gravity increases up to 7.3, and members at this end of the series are known as tantalite (feta2o6). specimens in which the iron is largely replaced by manganese are known as manganocolumbite or manganotantalite, according as they contain more niobium or more tantalum. columbite occurs as crystals and compact masses in granite and pegmatite at rabenstein in lower bavaria, the ilmen mountains in the urals, haddam in connecticut, and several other localities in the united states; also in the cryolite of greenland. tantalite is from finland, and it has recently been found in some abundance in the deposits of cassiterite in the tin-field of greenbushes in the blackwood district, western australia. [illustration: crystal of columbite.] dimorphous with columbite and tantalite are the tetragonal minerals tapiolite (= skogbolite) and mossite, so that the four form an isodimorphous group with the general formula (fe, mn) (nb, ta)2o6. mossite is from a pegmatite vein near moss in norway, and tapiolite is from finland. all these minerals contain tin in small amount. (l. j. s.)