Jacobsite

Jacobsite is a manganese iron oxide mineral. It is a magnetite spinel.It was first described in 1869 and named for the location of Jakobsberg, Sweden.
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General Information:
 Chemical Formula:
(Mn++,Fe++,Mg)(Fe+++,Mn+++)2O4
 Composition:
(Molecular Weight = 227.38 gm)
Magnesium 1.07 % Mg
Manganese 26.58 % Mn
Iron 44.21 % Fe
Oxygen 28.15 % O 
 Empirical Formula:
Mn2+0.6Fe2+0.3Mg0.1Fe3+1.5Mn3+0.5O4
 Locality:
Jakobsberg, Sweden.
 Name Origin:
Named after its locality.
Physical Properties:
 Cleavage:
None
 Color:
iron black or black.
 Density:
4.75
 Diaphaniety:
Opaque
 Habits:
Disseminated - Occurs in small, distinct particles dispersed in matrix., Massive - Granular - Common texture observed in granite and other igneous rock.,
 Hardness:
5.5-6 - Knife Blade-Orthoclase
 Luster:
Sub Metallic
 Streak:
reddish black
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