Bismuthian Stibiotantalite

$4,000

Bismuthian Stibiotantalite :

In stock

SKU: 51147 Locality: Ile-Ife Pegmatite District, Osun, Nigeria Dimensions: 9.8 X 6.7 X 5.4 cm

Description: 

In late 2018, a small number of very large, euhedral crystals of an unusual Nb-Ta oxide were discovered in a gem tourmaline pegmatite in the Ile-Ife LCT (Lithium-Cesium-Tantalum) pegmatite district in Oyo State, Nigeria. These crystals, some of which had previously been destroyed as Ta-Nb ore, were marketed by several Nigerian gemstone dealers. The crystals exhibit unusual morphology for orthorhombic Na-Tb oxides, with elongated, tapered terminal faces, and display a visually-striking color zonation, from translucent, smoke-gray and brown cores to opaque black rims. They are also very large and well-formed and represent some of the finest crystals known for these rare species. Representative core-to-rim samples from one of these large crystals (the crystal offered here) were subjected to EDX, XRD, and EPMA analyses. EPMA results show strong core-to-rim chemical zonation, from core zones with the formula of [Sb.89 Bi.13 ] [Ta.70 Nb.26 ] O4 to rims with a formula of [Sb.53-.59 Bi.38-.44 ] [Ta.97 Nb.03 ] O4. XRD data confirm that the crystals are dominated by stibiotantalite, which is Bi and Nb-rich in the core zones of these large crystals, with a progressive substitution of Bi for Sb, and Ta for Nb as one moves outward towards the rim of the crystals. This chemistry has not been described before in either stibiotantalite or bismutotantalite.

This is an outstanding example of a very rare species, of exceptional size and quality. At 9.8 cm tall and 1.47 kg in weight (amazingly dense due to the very high Tantalum content), this is an enormous crystal for this mineral. There is some damage to the back of the crystal but given its size and overall completeness (the damage is not visible when displayed as shown), I consider this excusable. A superb specimen for the serious collector of rare species or pegmatite minerals! Annette Slade photo.

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