Named for its tantalum content (of which it is the main ore), this mineral forms what is termed a solid solution series with a niobium rich end member called Columbite whereby these two elements are interchangeable in the crystal structure. In the mining business it is often found mixed together and referred to as coltan though Tantalite is much denser than Columbite. It is an essential ingredient of modern electronics and has been implicated in repeated and serious human rights abuses and slavery during Africa’s still ongoing (albeit at a lesser intensity) world war that raged in the eastern parts of the Democratic republic of Congo over the last couple of decades. There are various other qualifiers making it a double solution series, and the 4.0 x 3.3 x 3.0 cm Afghan specimen is actually Manganotantalite, its rosy hue imparted by a smidgen of manganese, with its opposite end members being iron or magnesium rich.
This is the prettier and gemmier end of the series with the iron rich member being dark and opaque while the manganese version is a lovely reddish brown and sometimes transparent, so faceted stones are sometimes cut for collectors (its Mohs hardness of 6.5 makes this easy to do though theplaes of weakness where there are less bonds in the crystal structure known as cleavage means that it muct be cut with care for the orientation). The mineral forms in pegmatites, those last bits of freezing granitic magma that distil rare elements which don’t fit into the crystal structures of the standard granitic minerals. It also occurs as placer deposits (from the Spanish for pleasure since they are easily mined) where rivers have concentrated dense minerals by winnowing out the lighter materials, often in potholes or other such places. It was named after Tantalus for its resistance to dissolution. As well as the localities already mentioned it is found in Brazil, Australia, Canada, Egyps, Nigeria, the USA and varied other places worldwide.
Image credit: Rob Lavinsky/iRocks.com