One of the ores of tungsten (as seen in old style light bulbs), like many metal minerals it forms a solid solution known as the Wolframite series (named for the intermediate compositions) between a manganese (called Hubnerite) and an iron end member (represented here), where the individual crystal can occupy any place along the spectrum of compositions between them. The crystals have a very bright lustre, and the usual colour is opaque black to very dark brown. Crystals are often flat tablets with lines down the long axis called striations. Like many metallic ores it is very dense in the hand, and fairly soft, with a hardness on Mohs scratch scale of 4.5.
It forms in high temperature hydrothermal veins, where the transporting superheated water was abruptly cooled, and in altered granites or pegmatites, usually as granular masses or slim prisms, though one example is known that precipitated directly from volcanic gases issuing from a fumarole (see http://bit.ly/131S7Aa for an explanation). It was first discovered in Spain (known as the type locality to the mineral world) in 1863 and named after a German mineralogist. As well as Spain this rarity is also found in Colorado, Bolivia, Russia, Korea and China, whence hails this rare 7.3 x 7.0 x 4.0 cm single striated crystal on the vein quartz in which it was born...
Loz Image credit: Joe Budd/Rob Lavinsky/iRocks.com
http://www.minerals.net/mineral/ferberite.aspx https://www.mindat.org/min-1476.html http://www.galleries.com/Ferberite http://www.mindat.org/min-1940.html http://www.galleries.com/Huebnerite http://bit.ly/1HVqYyi http://bit.ly/1D6g8Xi http://bit.ly/1InwgQd