Physical Properties of Tantalite
Tantalite is a dimorphic metal with another mineral called tapiolite. A dimorph is a mineral that has the same chemistry as another mineral but has a different structure.
Tantalum, a corrosion (heat and acid) resistant metal, is found primarily in the mineral group tantalite [(Fe, Mn)Ta2O6].
It is chemically similar to columbite, and the two are frequently grouped together in mineral guides as a semi-singular mineral called coltan or “columbite-tantalite.” Tantalite, on the other hand, has a much higher specific gravity than columbite (8.0+ vs. 5.2 for columbite). Tantalite-(Fe) or ferrotantalite is iron-rich tantalite, while tantalite-(Mn) or manganotantalite is manganese-rich tantalite.
It is a greyish silver, heavy, and extremely hard metal that is frequently found in association with fractionated pegmatites. Tantalum has been found in rare-element pegmatites that have been found throughout Manitoba’s Precambrian rocks.
Tantalite is found in granitic pegmatites rich in rare-earth elements, as well as placer deposits formed from such rocks. Australia, Brazil, Canada, Colombia (Guaina and Vichada), Egypt, northern Europe, Madagascar, Namibia, Nigeria, Rwanda, The Democratic Republic of the Congo, the United States (California, Colorado, Maine, and Virginia), and Zimbabwe have all been found to have it. Brazil has the world’s largest tantalite reserve (52.1%).
Tantalite is the most common tantalum mineral and an important source of the industrially useful metal.
Tantalite is used in alloys to increase strength and melting points, in glass to increase the index of refraction, and in surgical steel because it is non-reactive and does not irritate body tissues.
Tantalite is related to the mineral columbite. In fact, many mineral guides group the two together as a semi-singular mineral called columbite-tantalite.
A series occurs when two or more elements occupy the same positions within a crystal structure and their percentages vary. Because they have the same structure and chemistries, the two minerals in this series have similar properties (tantalum and niobium are very similar elements).
Tantalite is the tantalum-richer end member, while columbite is the niobium-richer end member. Niobium was previously known as columbium, hence the name columbite.
Tantalite differs most from columbite in that it has a much higher specific gravity, 8.0+ versus 5.2 for columbite. Color, transparency, and streak are other properties that vary slightly. Both minerals can be found in granitic pegmatites rich in lithium and phosphorus minerals, with columbite concentrated at the pegmatite’s edges and tantalite enriched in the core.
Tantalite has its own series. The amounts of iron and manganese vary greatly without having much of an effect on the properties. However, the two end members are recognized as distinct minerals, though collectors find this cumbersome and prefer tantalite to the non-unique names ferrotantalite and manganotantalite.
Tapiolite has a tetragonal structure as opposed to tantalite’s orthorhombic structure, despite having the same chemistry, (Fe, Mn)(Ta, Nb)2O6.
Where are Tantalite Found?
Tantalite specimens make an excellent addition to any mineral collection. Good crystals are both complex and visually appealing. Although the color range is typically limited to black to brown, the luster is generally satisfactory. Manganese rich tantalites can be brown and translucent.
Brazil and Australia have the world’s largest tantalum reserves. Rwanda, where the mineral is mined and imported, is one of the world’s major tantalum producers.
PHYSICAL CHARACTERISTICS OF TANTALITE
- The color ranges from dark black to iron-black to dark brown or even reddish brown.
- Luster can range from submetallic to almost resinous.
- Transparency: Crystals are nearly transparent in thin splinters, making them nearly opaque.
- The crystal system is orthorhombic, with dimensions of 2/m 2/m 2/m.
- Stubby prismatic crystals with complexly faceted or rounded terminations are examples of Crystal Habits. Very flat tabular crystals can also aggregate in parallel or nearly parallel groups. Granular and massive forms are also possible.
- Cleavage works in one direction.
- Subconchoidal fracture.
- When pure, the hardness is 6 – 6.5 and the specific gravity is approximately 8.0+. (very heavy for non-metallic minerals).
- The streak ranges from brownish-red to black.
Other characteristics include a bluish iridescent tarnish and weak magnetism in some specimens.
Albite, spodumene, cassiterite, microcline, lepidolite, apatite, beryl, microlite, tourmalines, and amblygonite are all associated minerals.
Newry, Maine; San Diego County, California; Colorado and Amelia, Virginia, USA; Renfrow County, Ontario, Canada; Madagascar; Sweden; Norway, and Finland are among the notable occurrences.
Crystal habit, streak, associations, and specific gravity are the best Field Indicators.
