Mineral Information and Data:

Columbite-(Mg)
MgNb2O6 [CNMNC approved formula]

Named as the magnesium-dominant member of the columbite group. First published in 1963. Name changed from magnocolumbite (IMA, 2008)

IMA status : Renamed IMA Approved; 2008 ()
CLASSIFICATION 
Dana
(8th edition) :
08.03.02.05  
  (08) Multiple Oxides with Nb, Ta, and Ti
  (08.03) where A (B2O6)
  (08.03.02) Tantalite - Columbite Series
  
Nickel-Strunz
(10th edition) :
04.DB.35
  (04) Oxides and Hydroxides
  (04.D) Metal:Oxygen = 1:2 and similar
  (04.DB) With medium-sized cations; chains of edge-sharing octahedra
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Crystal Habit: Rough crystals, tabular to acicular, to 1.5 cm, with nine forms noted.
Twinning: Common, with a 25° angle between extinction directions.
  
Color: Black to brownish black; brown, brownish red to reddish brown in transmitted light
Diaphaneity: Opaque, translucent on thin edges
Luster: Semimetallic
Hardness (Mohs): 6
Measured Density: 5.17 – 5.25 g/cm3
Cleavage: {100} and {001}
Fracture: Uneven
Streak: Dark brown
  
Geologic Setting: In a pegmatite in partially assimilated dolomitic marbles (Kukhi-Lal deposit,
Tajikistan).
Mineral Association: Ilmenorutile, cordierite, dravite, spinel, andalusite, kyanite (Kukhi-Lal deposit, Tajikistan).
  

 

Columbite-(Mg)
3x2x5 mm crystal of Columbite-(Mg) in quartz matrix from type locality. Induction striation, connected with simultaneous growth with the quartz, is well visible. Associating mineral is white agregate of hydromagnesite
Origin: Muzeinaya pegmatite vein, Gem spinel Deposit, Kukh-i-Lal (Kukhilal; Kuhi-lal), Pyandzh River Valley, Pamir Mts, Viloyati Mukhtori Gorno-Badakhshan (Viloyati Badakhshoni Kuni), Tajikistan
Photo and collection: © Pavel M. Kartashov

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