Ericssonite

Ericssonite
General
Category	Sorosilicates
Formula; (repeating unit)	BaMn2FeO[Si2O7](OH)
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) ; (same H-M symbol)
Space group	C2/m
Unit cell	a= 20.42, b= 7.03 ; c= 5.34 [Å], β= 95.5°; Z = 4
Identification
Color	deep reddish black
Crystal habit	Massive - uniformly indistinguishable crystals forming large masses
Cleavage	perfect, perfect on (100) fair on (011)
Tenacity	very brittle
Mohs scale hardness	4.5
Luster	sub metallic
Streak	brown
Diaphaneity	Translucent to opaque
Density	4.21
Refractive index	1.802-1.891
Pleochroism	x= pale greenish tan, y= red-brown, z= deep brown
Other characteristics	weakly magnetic

Ericssonite has a general formula of BaMn₂FeO[Si₂O₇](OH).[1] It was discovered in 1967 and named after John Ericsson (July 31, 1803 – March 8, 1889), a well known Swedish American inventor, engineer and designer of the iron-clad ship USS Monitor.[2] Ericssonite was discovered in the Jakobsberg Mine in Värmland, Sweden.[3]

Ericcsonite is monoclinic; this means it contains three unequal vectors, two of these vector angles are perpendicular while the other is at an angle greater than 90°.[4] Optically ericssonite is anisotropic which means that the mineral has more than one index of refraction, causing light to vary in speed depending on which axis it is traveling through. Since ericssonite is monoclinic, containing three unequal vectors, it has three indices of refraction. Ericssonite is usually a deep reddish-black in color. [5]

Ericssonite is only found in the Langban mine in Sweden, associated with a metamorphic manganese orebody. Also it is always inter-grown with orthoericssonite, which is almost identical to ericssonite except it contains extra silicon and oxygen in its chemical formula.

References

http://www.mindat.org/min-1397.html
"Ericssonite Mineral Data".
"Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden". Mindat.
Roberts, W.L., Campbell, T.J., and Rapp Jr, G.R. (1990) Encyclopedia of Minerals (2nd Edition). 294 p. Library of Congress Cataloging, Washington, D.C.
"The Truth About Ericcsonite".

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[1] ttp://www.mindat.org/min-1397.html

[2] "Ericssonite Mineral Data".

[3] "Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden". Mindat.

[4] Roberts, W.L., Campbell, T.J., and Rapp Jr, G.R. (1990) Encyclopedia of Minerals (2nd Edition). 294 p. Library of Congress Cataloging, Washington, D.C.

[5] "The Truth About Ericcsonite".