Jacobsite

Jacobsite is named after its discovery locality, at the Jakobsberg mine, near Stockholm, Värmland, Sweden.

Jacobsite forms opaque to translucent, black to brownish black crystals or coarse to fine granular masses with metallic to submetallic lustre.
General Information
Chemical Formula
(Mn
2+
 
,Fe
2+
 
,Mg)(Fe
3+
 
,Mn
3+
 
)
 
2
O
 
4
Anthony et al, Handbook of mineralogy (2001)
Photos of natural/un-cut material from mindat.org
Physical Properties of Jacobsite
Mohs Hardness5.5 to 6.5
Anthony et al, Handbook of mineralogy (2001)
Specific Gravity4.76 to 5.03
Anthony et al, Handbook of mineralogy (2001)
Optical Properties of Jacobsite
Optical CharacterIsotropic
Anthony et al, Handbook of mineralogy (2001)
Colour
Colour (General)Black to brownish black; grayish white with olive tint in reflected light, with brown internal reflections.
Anthony et al, Handbook of mineralogy (2001)
TransparencyTranslucent,Opaque
Anthony et al, Handbook of mineralogy (2001) Opaque, translucent on thin edges
LustreDull (Earthy),Metallic,Submetallic
Anthony et al, Handbook of mineralogy (2001) Metallic, splendent to semimetallic, dull
Crystallography of Jacobsite
Crystal SystemIsometric
Anthony et al, Handbook of mineralogy (2001)
HabitRarely in octahedral crystals, to 4 mm, which may exhibit exsolved hausmannite or galaxite; coarse to fine granular, massive.
Anthony et al, Handbook of mineralogy (2001)
Geological Environment
Where found:A primary mineral or an alteration product of other manganese-bearing minerals in some metamorphosed manganese deposits.
Anthony et al, Handbook of mineralogy (2001)
Further Information
Mineral information:Jacobsite information at mindat.org
Copyright © Jolyon & Katya Ralph 1993-2020. Site Map. Locality, gem & photograph data are the copyright of the individuals who submitted them. For more information please contact the . Gemdat.org is an online information resource dedicated to providing free gemmological information to all.