Niobates-Tantalates, Columbite-Tantalite Composition & Structure

Columbite-Tantalite

Composition. A niobate and tantalate of ferrous iron and manganese (Fe,Mn) (Nb,Ta)2O6 which varies in composition from the niotable, columbite (Fe,Mn)Nb₂O₆, to the tantalate, tantalite (Fe,Mn)Ta₂O₆. often contain small amounts of tin, tungsten, etc. A variety known as manganese.

Crystallization. Orthohombic. Habit of crystals is short prismatic; often in square prisms because of prominent development of the vertical pinacocoids. Terminated by basal plane, pyramids and domes; frequently complex. At times in heart-shaped contact twins.

Structure. Crystallized and in parallel crystals groups. Also frequently granular massive.

Physical properties. H. = 6. G. = 5.3-7.3, varying with the compodition,increasing with rise in precentage of tantalum oxide present. Submetallic luster. Color iron-black, frequently iridescent. Streak dark red to black.

Test. Dificultly fusible (5-5.5). Fused with borax; the bead disloved in ydrochloric acid; the solution boiled with tin gives a blue color (niobium). There is no simple test for tantalum. Generrally when fused in O. F. With sodium carbonate on charcoal in R. F. Yields a magnetic mass. Recognized usually by its black color, submetallic streak and high specifec gravite.

Ocurrence. Occur in granite rocks and in pegmatite veins, associated with quartz, feldspar, mica, tuormaline, berly, spodumene, cassiterite, samarskite, wolframite, microlite, monazite, etc. Notable localities for its occurrence are the wefst coast of Greenland; near Moss, Norway; Bodennais, Bavaria; Ilmen Mountains, Russia; Western Australia (manganotantalite); mandagascar; Standish, Maine; Haddam, Midletown and Brabchyville, Connectituc; in Amelia County, Virginia; Mtchell County, North Carolina; Black Hills, Sount Dakota; near canon City, Colorado.

Name. They two names are derived from the acid elements that the minerals contain. Niobium is often called columbium.

Use. Sours of tantalum, which has been used in makinng filaments for incandencent electric lamps. Tantalum is also a constiuent various iron allosys.

There a number of other niobates and tantalates, all of with are rare in occurrence. The following, however, might be mentioned: pyrochore, chiefly a niobate of the cerium metals and calcium; microlite, essentially Ca₂Ta₂O₇; fergusonite, a niobite of yttrium, cerium, uranium, etc., samarshitea, a niobate and tantalate of ferrous iron, uranium and the cerium metals.