Tantalite-(Mg)
The mineral group tantalite [(Fe, Mn)Ta2O6] is the primary source of the chemical element tantalum, a corrosion (heat and acid) resistant metal. It is chemically similar to columbite, and the two are often grouped together as a semi-singular mineral called coltan or "columbite-tantalite" in many mineral guides. However, tantalite has a much greater specific gravity than columbite (8.0+ compared to columbite's 5.2). Iron-rich tantalite is the mineral tantalite-(Fe) or ferrotantalite and manganese-rich is tantalite-(Mn) or manganotantalite. Tantalite is also very close to tapiolite.
Intro adapted from Wikipedia (CC BY-SA).
Tantalite-(Mg) is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MgTa₂O₆.
It crystallizes in the orthorhombic crystal system (space group Pbcn). It is a member of the Columbite structural group.
Key properties: Mohs hardness 5.5; specific gravity 6.7; Brown-red streak; Semi-metallic to metallic luster.
IMA symbol Ttl-Mg, IMA status: approved, named in 2002.
Occurs as replacement rims on tantalite-(Mn) crystals in deeply desilicated granite pegmatite that cuts serpentinite near its contact with marble.
It is found associated with Tantalite-(Fe), columbite-(Fe), microlite, calcite, sodic plagioclase.
Suffix for dominant Mg in the composition and relation to tantalite-(Fe) and tantalite-(Mn), named for the Greek mythical Tantalus, for the difficulty in bringing the mineral into solution.