Native element, transition metal
Tantalum rarely occurs in the native state. In compounds its most common oxidation state is Ta5+ but other states from Ta-3 to Ta5+ are also possible. The oxidation state for all naturally occurring minerals is Ta5+. The most common ore of tantalum is tantalite (Wiki).
Specific gravity: 16.6
Colour: Grey, blue-grey
Solubility: Tantalum is highly resistant to corrosion by acids; at temperatures below 150oC it is almost completely immune to attack by the normally corrosive aqua regia. It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulphfur trioxide, as well as with a solution of potassium hydroxide (Wiki)
Melting point: 3017oC is exceeded among the elements only by tungsten, rhenium, osmium and carbon (Wiki)
Boiling point: 5458oC (Wiki)
Abundance: 1.7 parts per million by mass, 0.2 parts per million by moles, in the Earth's crust (ChC).
On a hill between the Osimovka and Abramovka rivers, southern Primorsky Krai, Russia, more than 20 grains of tantalum have been found with other native metals, including niobium, tungsten, nickel, aluminium and silicon, in eluvial sediments overlying kaolinitised schist. Native tantalum has been independently reported to occur as inclusions in diamond (AM 84.992).
Tantalum-bearing minerals include:
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