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Encyclopedia Britannica - Main :: CLI-COM |
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COLUMBITE , a rare mineral
tantalum respectively, the general formula
mineral
Charles Iatchett discovered, in 18or, the element
system
brilliant with a sub-metallic lustre. Twinned crystals are not uncommon, and there is a distinct cleavage parallel to the face marked bin 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
district
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
Moss
Finland
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