Chamosite
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Chamosite was named in 1820 by Pierre Berthier for the type locality Haut de Cry, near Chamoson, Valais, Switzerland.

Discovered in 1820; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Fe²⁺,Mg)₅Al(AlSi₃O₁₀)(OH)₈

Iron Magnesium Aluminum Silicate Hydroxide

Molecular Weight:

664.18 gm

Composition:

Magnesium

5.49 %

Mg

9.10 %

MgO

Aluminum

8.12 %

Al

15.35 %

Al₂O₃

Iron

29.43 %

Fe

32.45 %

FeO / 6.01 % Fe₂O₃

Silicon

12.69 %

Si

27.14 %

SiO₂

Hydrogen

 0.91 %

H

8.14 %

H₂O

Oxygen

43.36 %

O

100.00 %

98.19 %

= TOTAL OXIDE

Classification

Mineral Classification:

SILICATES (Germanates)

Strunz 8th Ed. ID:

8/H.23-30

Nickel-Strunz 10th Ed. ID:

9.EC.55

9 : SILICATES (Germanates)
E : Phyllosilicates
C : Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

Related to:

Chlorite Group. The iron(II) analogue of Clinochlore. Chamosite-Clinochlore Series. Dimorphous with Orthochamosite.

Members of Group:

Chlorite Group: Baileychlore, Borocookeite, Chamosite, Clinochlore, Cookeite, Corundophilite, Donbassite, Franklinfurnaceite, Nimite, Orthochamosite, Pennantite, Sudoite 

Varieties:

Bavalite, Corundophilite, Daphnite, Pseudothuringite, Thuringite

Synonyms:

Brunsvigite, Daphnite, Delessite, Thuringite (Fe)

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

In scaly aggregates, foliated or granular; oolitic, made up of very minute radiating crystals; massive.

Twinning:

Twin and composition plane {001}, axis [310] 

Physical Properties

Cleavage:

Perfect on {001} 

Fracture:

Irregular/uneven

Tenacity:

Somewhat flexible but inelastic.

Moh's Hardness:

2.0 - 3.0

Density:

3.00 - 3.40 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Weakly magnetic

Optical Properties

Color:

Green, greenish grey, black, brown; in thin section, colorless, yellowish, green

Transparency:

Translucent to opaque

Luster:

Pearly

Refractive Index:

1.600 - 1.670  Biaxial ( - )

Birefringence:

0.070

Dispersion:

Strong; r < v

Pleochroism:

Weak to moderate; X = yellow-green to light brownish green; Y = Z = green to dark green.

Occurances

Geological Setting:

In sedimentary ironstones; authigenically formed under reducing conditions in the presence of decomposed organic material.

Common Associations:

Siderite, Kaolinite, Quartz, Magnetite, Pyroxenes, Plagioclase, Olivine, Calcite

Common Impurities:

Mn, Ca, Na, K

Type Locality:

Haut de Cry, Chamoson, Wallis (Valais), Switzerland

Year Discovered:

1820

View mineral photos:

Chamosite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Chamosite is the iron rich end member of the Chlorite Group of minerals that includes Chamosite, Clinochlore and Cookeite among others. Chamosite was discovered and named in 1820 by Pierre Bertier, a mineralogist and mining engineer from Nemours, France. It was discovered at Haut de Cry, near Chamoson, Valais, Switzerland and named after the nearby municipality of Chamoson. The new mineral was found in an area of low to moderate grade metamorphosed iron deposits as gray or black crystals in oolitic iron ore. Chamosite may be green, gray-green, brown or black with pearly luster and is also weakly magnetic.

Locations for Chamosite: Many localities, but careful characterization is necessary. From Chamoson, Valais, and in the Maderantal, Uri, Switzerland. At He·rmanovice and Kladno, Czech Republic. From Schmiedefeld, near Suhl, and Schleiz, Thuringia, Germany. In England, at Frodingham, Lincolnshire; Wickwar, Gloucestershire; at Penzance, Cornwall, and elsewhere. At Knowehead, County Antrim, Ireland. In the Arakawa mine, Akita Prefecture, and at Shogase, Tokushima Prefecture, Japan. From Creede, Mineral County, Colorado; near Hot Springs, Garland County, Arkansas; and in the Beacon Hill mine, Champion, Marquette County, Michigan, USA. At Wabana, Newfoundland, Canada.
 

  
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