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Formula: Ca3V3+2(SiO4)3
Nesosilicate (insular SiO4 groups), garnet group,
vanadium-bearing mineral
Crystal System: Isometric
Specific gravity: 3.74 to 3.77 measured, 3.76 calculated
Hardness: 6 to 7
Streak: White
Colour: Green, brownish green
Luminescence: No fluorescence under UV
Common impurities: Cr,Mn,Mg
Environments
Sedimentary environments
Metamorphic environments
Localities
At Coat an Noz, Belle-Isle-en-Terre, Guingamp, Côtes-d'Armor, Brittany, France,
vanadium-rich garnets belonging to
the continuous solid-solution grossular-goldmanite series are
found within metamorphosed calcareous metapelites derived from
euxinic (Pertaining to a rock facies that includes black shales and
graphitic sediments of various kinds) sediments. Associated
clinopyroxenes and actinolites
show significant vanadium contents. In
skarns developed from similar
metapelites, goldmanite-rich
garnets form the cores of crystals surrounded by
grossular overgrowths.
(AM 74: 852-858).
Associated minerals include plagioclase,
titanite, clinopyroxene,
actinolite, chlorite,
pyrite and arsenopyrite
(HOM).
At the Yamato mine, Yamato village, Oshima District, Kagoshima Prefecture, Japan, goldmanite is associated
with rhodonite and braunite
(HOM).
At the Deokpyeong area, Gyeonggi Province, South Korea, goldmanite was found as subrounded green
porphyroblasts ranging from 0.1 to 1.7 mm in size in the carbonaceous black
slates. A radiating aggregate of slightly curved blades of
goldmanite crystals replaces the fine-grained black matrix. The black
slate in the Deokpyeong area is the richest known accessible source of
relatively pure goldmanite
(MM 63.253-256).
At Rybníček, Pezinok, Pezinok District, Bratislava Region, Slovakia, mineralisation has been studied in carbon-rich
amphibole schists with
pyrite and pyrrhotite. The study
has revealed the presence of vanadium- and
chromium- rich garnet,
clinozoisite and muscovite,
associated with amphiboles
(magnesio-hornblende,
tremolite, actinolite and
edenite), diopside and
albite. The garnet contains
goldmanite, uvarovite and
grossular end-members.
The vanadium- and chromium- rich
clinozoisite to mukhinite were
metamorphosed with crystallisation of vanadium- and
chromium- rich silicates, diopside,
amphiboles, phlogopite,
titanite, albite,
quartz, carbonate, pyrite and
pyrrhotite. A later retrograde metamorphism is connected with production
of vanadium- and chromium- poor
muscovite, clinochlore,
clinozoisite,
pumpellyite-(Mg),
prehnite, quartz and carbonates,
under prehnite-pumpellyite facies conditions
(AM 93.63-73).
At the type locality, an unnamed prospect pit, Sandy Mine, Laguna subdistrict, Cibola County, New Mexico, USA,
the small metamorphosed
uranium-vanadium deposit exposed
in the prospect pit is in sandstone, overlain by relatively
unmineralised limestone 2 to 3 feet thick, which is overlain by a
dolerite sill about 20 feet thick.
Quartz forms about 85 per cent of the detrital fraction of the
sandstone; microcline
and fragments that are too altered for identification form the remaining 15 per cent.
Vanadium clay from the mine
area is composed of mica (probably
roscoelite) and
montmorillonite. Uraninite
and coffinite have been oxidised at this location but
vanadium clay has resisted
oxidation.
Common garnet is disseminated through the
sandstone and encrusts joint surfaces, but goldmanite is
confined to the dark layers of sandstone rich in
vanadium clay.
Garnet that encrusts joint surfaces contains little
vanadium and is probably
andradite-grossular.
Goldmanite in the prospect pit is fine-grained, rarely exceeding 0.1 mm in size. It is generally free of
impurities, and unzoned. Where associated with vanadium
clay, goldmanite is anhedral; where embedded in
calcite, it is euhedral; many small crystals of goldmanite exhibit
sharply defined dodecahedral faces
(AM 49.644-655).
Associated minerals include quartz,
calcite, diopside,
vesuvianite, wollastonite,
epidote,
grossular-andradite,
biotite, spinel,
plagioclase, pyrrhotite,
roscoelite and
montmorillonite
(HOM).
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