Columbite

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Columbite-(Fe)
Columbite.jpg
General
Category Oxide minerals
Formula
(repeating unit)
Fe2+Nb2O6
Strunz classification 04.DB.35
Identification
Color Black, brownish black.
Crystal habit Massive - Granular - Common texture observed in granite and other igneous rock; Striated - Parallel lines on crystal surface or cleavage face.
Crystal system Orthorhombic, (2/m 2/m 2/m), SpaceGroup = Pcan
Cleavage [010] Distinct
Fracture Sub Conchoidal - Fractures developed in brittle materials characterized by semi-curving surfaces.
Mohs scale hardness 6
Luster sub-metallic
Streak blackish brown
Specific gravity 5.3 - 7.3, Average = 6.3
Optical properties Biaxial (+), b=2.29-2.4
Other characteristics non-radioactive, non-fluorescent.
References [1][2]

Columbite, also called niobite, niobite-tantalite and columbate [(Fe, Mn)Nb2O6], is a black mineral group that is an ore of niobium. It has a submetallic luster and a high density and is a niobate of iron and manganese. This mineral group was first found in Haddam, Connecticut, in the United States. It forms a series with the tantalum-dominant analogue ferrotantalite and one with the manganese-dominant analogue manganocolumbite. The iron-rich member of the columbite group is ferrocolumbite. Some tin and tungsten may be present in the mineral. Yttrocolumbite is the yttrium-rich columbite with the formula (Y,U,Fe)(Nb,Ta)O4. It is a radioactive mineral found in Mozambique.

Columbite has the same composition and crystal symmetry (orthorombic) as tantalite. In fact, the two are often grouped together as a semi-singular mineral series called columbite-tantalite or coltan in many mineral guides. However, tantalite has a much greater specific gravity than columbite, more than 8.0 compared to columbite's 5.2.[3]

Columbite is also very similar to tapiolite. Those minerals have same chemical composition but different crystal symmetry: orthorhombic for columbite and tetragonal for tapiolite.[4] The largest documented single crystal of columbite consisted of plates 6 millimetres (0.24 in) thick measuring 76 by 61 centimetres (30 in × 24 in).[5]

The occurrence of columbite in the United States was made known from a specimen sent by Governor John Winthrop of Connecticut to Hans Sloane, President of the Royal Society of Great Britain.[6]

In 1801 Charles Hatchett discovered the element niobium in columbite, which he named columbium after Columbia, a historical and poetic name for the USA.[7]

See also[edit]

References[edit]

  1. ^ Columbite-(Fe) Mineral Data
  2. ^ Columbite-(Fe) on Mindat.org
  3. ^ mindat.org Tantalite
  4. ^ P. Cerny et al. "The tantalite-tapiolite gap: natural assemblages versus experimental data" Canadian Mineralogist 30 (1992) 587 free download
  5. ^ P. C. Rickwood (1981). "The largest crystals". American Mineralogist 66: 885–907. 
  6. ^ Wikisource-logo.svg "Columbite". New International Encyclopedia. 1905. 
  7. ^  Chisholm, Hugh, ed. (1911). "Columbite". Encyclopædia Britannica (11th ed.). Cambridge University Press.