Stibiotantalite
Stibiotantalite is a mineral consisting of (antimony, tantalum or niobium, and oxygen). It is found in complex granite pegmatites. If the quantity of niobium exceeds the tantalum content, the mineral is called stibiocolumbite. It is translucent to transparent, medium hard (5.5 mohs), appears yellow to dark brown, reddish or greenish brown, with an adamantine luster. Stibiotantalite is found in veins and walls associated with tin mines. It is a fairly rare to rare mineral. Due to its relative softness, it is more likely to be found in mineral collections than in jewelry.