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Formula: Mn2+Nb2O6
Multiple oxide containing niobium and
manganese, columbite group, forms
series with columbite-(Fe) and with
tantalite-(Mn)
Specific gravity: 5.28
Hardness: 6
Streak: Dark red to black
Colour: Black to brownish black, dark red-brown, reddish brown in transmitted light
Environments:
Columbite-(Mn) occurs as an accessory and primary constituent of
granite
pegmatites, or in placers. Associated minerals include
albite, microcline,
beryl, lepidolite,
muscovite, tourmaline,
spodumene, lithiophilite, triphylite, amblygonite,
triplite, apatite,
samarskite, microlite and
cassiterite
(HOM). The pure end-member is not found in nature, although it has been synthesised
(Dana).
Localities
The Koktokay No. 3 pegmatite, Altay Mine, Koktokay pegmatite field, Fuyun county, Aletai Prefecture, Yili Hasake
Autonomous Prefecture, Xinjiang, China, hosts many minerals including columbite-(Mn)
(Extra Lapis Beryl p67).
The Pulsifer pegmatite, West Mount Apatite Mining District, Auburn, Androscoggin county, Maine, USA, is a rare-element
granitic
pegmatite that intrudes upper
amphibolite facies
metapelites and biotite
schists that are locally interbedded with
calc-silicate rocks. The
pegmatite exhibits five distinct zonations.
The border zone consists of fine to mediumgrained equi-granular quartz and
plagioclase, and minor biotite and
almandine.
The wall zone consists of slightly graphic K-feldspar,
quartz, biotite and
almandine.
The first intermediate zone is characterised by coarse-grained graphic feldspar
and plumose muscovite-quartz
aggregates.
Almandine and schorl are found as
accessory minerals, and rare beryl has been observed.
The first intermediate zone grades irregularly into a coarse-grained
plagioclase plus quartz plus
muscovite second intermediate zone.
The pocket zone assemblage, which lies below the second intermediate zone and immediately above the
garnet seam, consists primarily of
cleavelandite and quartz, although
locally blocky K-feldspar and
muscovite are also abundant. Gem
tourmaline, beryl,
fluorapatite,
hydroxylherderite, gahnite,
almandine, columbite-(Mn) and
cookeite are among the minerals that have been found within the pocket zone.
The garnet seam is a 1 to 5 cm thick layer of 2 mm to 3 cm euhedral
almandine plus anhedral smoky quartz.
Just below the garnet seam lies a zone of undetermined thickness that is composed
primarily of blocky graphic albite.
Rare columbite-(Mn) is the most prominent
niobium-tantalum oxide mineral
present
(R&M 97.1.8-11).
The Emmons pegmatite, Greenwood, Oxford county, Maine, USA, is situated in a belt of metasedimentary rocks which
originated as marine sediments which were subsequently deformed and metamorphosed. It is an example of a highly evolved
boron, lithium,
cesium and tantalum enriched
pegmatite. Columbite-(Mn) crystals with a blocky habit
have been noted in the intermediate zone as well as in small miarolitic cavities in the
albite replacement units. Some of the crystals also exhibit a striking blue
tarnish. Crystals usually range from 1 mm to 2 cm in size. Higher manganese
content results in a brown hue, and a blockier habit is usually associated with elevated
tantalum content
(R&M 94.6.506).
At the Chickering Mine, Walpole, Cheshire county, New Hampshire, USA, columbite-(Mn) microcrystals have been sparingly
found embedded in quartz, the largest being 3.5 mm in length. The crystals
are black and are well-formed prismatic or flat tabular in habit
(R&M 90.415).
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