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Formula: (Fe2+,Mg,Al,Fe3+)6(Si,Al)4O10(OH,O)8
Phyllosilicate (sheet silicate), chlorite group, forms a series with
clinochlore
Thuringite is a ferroan variety of chamosite
Specific gravity: 2.95 to 3.30
Hardness: 3
Colour: Green, grey-green, black
Solubility: Decomposed by hot hydrochloric acid (Dana)
Common impurities: Mn,Ca,Na,K
Environments:
Plutonic igneous environments
Pegmatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments
Basaltic cavities
Chamosite occurs in many different environments:
- In granitic bodies formed by the hydrothermal alteration of
micas
such as biotite
(Mines and Minerals 25.27).
- In granite pegmatites
(Dana).
- In sedimentary ironstone (HOM). Abundant in soils and marine
clays. Found in coal deposits
(Dana).
- Authigenically formed under reducing conditions in the presence of decomposed organic material
(HOM).
- Formed in low-grade regional and
contact metamorphosed rocks
(Dana).
- As a hydrothermal alteration of wall rock around sulphide deposits
(Dana).
- In amygdules in volcanic rocks
(Dana).
Chamosite has been found as a replacement of a wide variety of silicates, including
garnet
(Dana).
Associated minerals include siderite,
kaolinite, quartz,
magnetite, pyroxene,
plagioclase, olivine,
calcite, feldspar,
garnet, muscovite,
biotite, amphibole,
pyroxene, dolomite,
chromite, talc,
serpentine,
chloritoid, ilmenite,
titanite, zircon,
zeolites, tourmaline,
hematite and rutile.
(Dana, HOM)
Localities
The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia,
are skarn deposits at the contact between
granodiorite and volcanic rocks.
Magnesian chamosite is a primary silicate that has been
found in magnetite-rich skarn
associated with chlorite
(AJM 22.1.33).
At Girardville, Quebec, Canada, chamosite is found at the contact with the enclosing
gneiss and in altered zones of the pegmatite.
Hematite is generally found on its surface
(R&M 88.5.431).
At Saint-Pierre-de-Broughton, Quebec, Canada, chamosite occurs in the
albite-stilpnomelane
schist and carbonate rock contacts. It is common
in the anatase- and
brookite-bearing fissures, often forming
coatings on and inclusions in albite,
anatase, brookite,
and quartz
(R&M 85.6.503).
At the Yaogangxian mine, Hunan, China, chamosite occurs on quartz
(R&M 85.4.320).
At the Braen quarry, Passaic county, New Jersey, USA, chamosite has been found as
pseudomorphs after
analcime and natrolite
(Minrec 40.6.516).
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