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Formula: Mn(CO3)
Carbonate of manganese,
calcite group
Crystal System: Trigonal
Specific gravity: 3.7 measured, 3.7 calculated
Hardness: 3½ to 4
Streak: White
Colour: Rose-pink, light red, yellowish grey, brownish
Solubility: Slightly soluble in water with the
solubility rate increasing with the presence of CO2. Begins to dissociate at
about 300˚ with the formation of CO2 and MnO. Moderately soluble in hydrochloric, sulphuric and nitric
acid.
Common impurities: Fe,Ca,Mg,Zn,Co,Cd
Environments:
Pegmatites
Metamorphic environments
Hydrothermal environments
Rhodochrosite is a comparatively rare mineral, occurring as a
primary mineral in
epithermal (low temperature),
mesothermal (moderate temperature) and
hypothermal (high temperature) hydrothermal veins, with ores of
silver, lead,
copper,
and other manganese minerals. It also occurs as large deposits in metamorphic rocks, and the alkaline syenite pegmatites of
Mont Saint-Hilaire, Canada
(R&M 93.2.147)
Localities
At Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, rhodochrosite
pseudomorphs after fluorite and after
serandite have been found
(KL p162, 163).
At the Wutong Mine, Liubao, Cangwu County, Wuzhou, Guangxi, China, rhodochrosite occurs both as well formed, red rhombs up
to several cm in size, and
also as pink crystals on a grey limestone matrix, associated with colourless
quartz, gold-coloured pyrite and a dark grey
mineral that
may be hübnerite
(AESS)
Rhodochrosite Rhomb from Wutong - Image
Rhodochrosite on matrix from Wutong - Image
At the Dongpo ore field, Yizhang County, Chenzhou, Hunan, China, crystalline pink rhodochrosite has been found, coloured
black in parts by manganese oxides
(AESS).
Rhodochrosite from Dongpo - Image
At Yaogangxian Mine, Yaogangxian W-Sn ore field, Yizhang County, Chenzhou, Hunan, China, red crystalline rhodochrosite has
been found
(AESS).
Rhodochrosite from Yaogangxian - Image
At the Oppu mine, Japan, rhodochrosite pseudomorphs after
calcite have been found
(KL p161).
At Charcas, Charcas Municipality, San Luis Potosí, Mexico,
the primary minerals are
sphalerite, galena,
chalcopyrite, bornite,
tetrahedrite,
arsenopyrite, pyrite and
silver minerals such as jalpaite,
diaphorite and acanthite. In
the host rock, as metamorphic or alteration minerals, danburite,
datolite, hedenbergite,
epidote, chlorite,
andradite, actinolite
and wollastonite have been reported.
Quartz, calcite and
danburite crystallised during the entire life of the systems, throughout
the intrusive emplacement, metamorphism, and mineralising events. With depth, both
sphalerite and galena decrease
while chalcopyrite increases.
Secondary sulphides formed include
bornite, covellite,
digenite and chalcocite.
Native silver, native gold,
hematite and goethite were
deposited after the sulphides
(Minrec 55.6.727-728).
Rhodochrosite is deep pink and forms millimetre-size bladed crystals in aggregates and coatings up to several
millimeters thick on other minerals. A few specimens have been found where rhodochrosite forms an undulating
carpet to 3 cm thick, covering grey-green datolite with associated
pyrite, chalcopyrite and
calcite
(Minrec 55.6.769).
Rhodochrosite from Charcas - Image
The type locality is the Cavnic Mine, Cavnic, Maramureș County, Romania.
Rhodochrosite from Cavnic - Image
At the NChwaning mine, Kalahari manganese fields, South Africa, rhodochrosite
pseudomorphs after sturmanite and
andradite pseudomorphs after
rhodochrosite
have been found
(KL p164).
At the Magma mine, Pioneer District, Pinal county, Arizona, USA, rhodochrosite has been found in the matrix of
groutite specimens, and as massive material associated with
chalcopyrite
(R&M 95.1.87).
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, rhodochrosite occurs as crystals to 3 cm in
miarolitic cavities,
and as masses in phosphate pods. In a large mass of rhodochrosite-siderite after
lithiophilite, millimeter-sized
sphalerite
crystals associated with perloffite have been noted. The Emmons pegmatite is
an example of a highly evolved
boron-lithium-cesium-tantalum
enriched pegmatite
(R&M 94.6.514).
Near the contact with lithiophilite the rhodochrosite crystals are partially replaced
by hureaulite and reddingite. Near the top of the
lithiophilite in some areas rhodochrosite replaces
lithiophilite. Associated with this replacement rhodochrosite are several manganese-rich
phosphates, including strunzite, jahnsite-group
species, pseudolaueite, laueite and
stewartite
(R&M 95.2.166).
At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the
pegmatites are beryl-type
rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most
complex zonation and diverse mineralogy of any of the Keyes
pegmatites. Six zones are distinguished, as follows, proceeding
inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase
border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite
wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite
outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite
middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to
1.2 meters in size that were altered to vuggy
albite-muscovite with
fluorapatite crystals. This unit presumably was the source of the
albite, muscovite,
fluorapatite, quartz and other
crystallised minerals found in pieces of vuggy albite
rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including
tourmaline, graftonite,
triphylite, vivianite,
pyrite, pyrrhotite, and
beryl crystals to 30.5 cm long and 12.7 cm across.
One specimen of rhodochrosite is known from the Keyes mines. It is a miniature of bladed pink rhodochrosite
with minor blue-green fluorapatite in a
quartz-albite-muscovite
matrix
(R&M 97.4.323).
At the Burgin Mine, East Tintic Mining District, Utah County, Utah, USA, rhodochrosite occurs as pale pink to
medium pink rhombohedral crystals; some appear to be stalactite/stalagmite formations, intergrown in some cases with
pyrite and tetrahedrite
crystals
(MinRec 55.2.220).
Rhodochrosite from the Burgin Mine -
Image
Alteration
braunite and CO2 to rhodochrosite,
rhodonite
and O2
2Mn2+Mn3+6O8(SiO4) + 12CO2 ⇌ 12MnCO3 +
2Mn2+SiO3 + 3O2
Increasing temperature favours the forward reaction
(AM80.571).
rhodochrosite to manganosite and CO2
MnCO3 ⇌ MnO + CO2
Increasing temperature favours the forward reaction
(AM80.571).
rhodochrosite and O2 to bixbyite-(Mn) and CO2
4MnCO3 + O2 ⇌ 2Mn3+2O3 +4CO2
Increasing temperature favours the forward reaction
(AM80.571).
rhodochrosite and O2 to hausmannite and CO2
6MnCO3 + O2 ⇌ 2Mn2+Mn3+2O4 +6CO2
(AM80.571)
rhodochrosite and O2 to pyrolusite and CO2
2MnCO3 + O2 ⇌ 2Mn4+O2 + 2CO2
(AM80.571)
rhodochrosite and quartz to rhodonite and
CO2
MnCO3 + SiO2 ⇌ Mn2+SiO3 + CO2
This is a metamorphic reaction occurring in manganese deposits and manganese-rich iron formations. Increasing temperature
favours the forward
reaction
(MOM p487, AM80.571).
rhodochrosite, SiO2 and O2 to braunite and CO2
14MnCO3 + 2SiO2 + 3O2 ⇌ 2Mn2+Mn3+6O8(SiO4)
⇌ 14CO2
Increasing temperature favours the forward reaction
(AM80.571).
rhodonite and rhodochrosite to
tephroite
and CO2
Mn2+SiO3 + Mn(CO3) ⇌ Mn2+2(SiO4) +
CO2
Increasing temperature favours the forward reaction
(DHZ 1A p344, 348, AM80.571).
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