Yttrio-tantalite

The present remarkably fine specimen of Yttrio-tantalite, from Ytterby in Sweden, is in the collection at the British Museum. The substance is dispersed through Feldspar, Quartz, and Mica, in a manner very much resembling Feldspar in some Porphyrys, apparently in imperfect crystals, crossing, and were it white or reddish instead of a fine coal black, it might have been passed over as Feldspar in Porphyry. It does not appear that any one has been able to discover the form of the crystal, and it can only be understood in part without spoiling the present specimen. We however venture a hint at its form in the outline below collected from various sections shown on the specimen. It appears to be a rhomboidal prism terminated at each cut by two rectangular faces. The hardness is moderate; in general it opaque, with the blackness and lustre of coal, but sometimes transparent and greenish brown in small fragments. The fracture is rather splintery and resinous. Spec. Grav. 5.130. According to its discoverer it is composed of Tantalium united to Yttria and Iron; according to Vauquelin it contains Oxide of Tantalium 45, and the remainder Yitria and Iron.