A primary mineral or and alteration product of othe rmanganese-bearing minerals in some metamorphosed Mn deposits. Dimorphous with iwakiite and forms a series with magnetite.
IMA Status:
Valid Species (Pre-IMA) 1869
Locality:
Jakobsberg, Sweden. Link to MinDat.org Location Data.
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Physical Properties of Jacobsite
Cleavage:
None
Color:
Iron black, Black.
Density:
4.75
Diaphaneity:
Opaque
Fracture:
Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Habit:
Disseminated - Occurs in small, distinct particles dispersed in matrix.
Habit:
Massive - Granular - Common texture observed in granite and other igneous rock.
Hardness:
5.5-6 - Knife Blade-Orthoclase
Luster:
Sub Metallic
Magnetism:
Weakly magnetic
Streak:
reddish black
Optical Properties of Jacobsite
Gladstone-Dale:
CI meas= 0.01 (Superior) - where the CI = (1-KPDmeas/KC) CI calc= 0.044 (Good) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2642,KPDmeas= 0.2737,KC= 0.2764 Ncalc = 2.31 - 2.36
Optical Data:
Isotropic, n=2.3.
RL Color:
Grayish with with olive tint and brown internal reflections.
Reflectivity
Standardized Intensity (100%) Reflection Spectra of Jacobsite in Air
λ
R
∑ R(λ)
400 nm
19.00
420 nm
18.80
440 nm
18.60
460 nm
18.40
480 nm
18.20
500 nm
18.10
520 nm
18.00
540 nm
17.80
560 nm
17.60
580 nm
17.40
600 nm
17.20
620 nm
17.00
640 nm
16.80
660 nm
16.60
680 nm
16.50
700 nm
16.40
Calculated Relative Intensity Colors of Jacobsite in Air
Relative Intensity
0%
60%
100%
120%
180%
240%
300%
360%
420%
480%
510%
R
Calculated Properties of Jacobsite
Electron Density:
Bulk Density (Electron Density)=4.49 gm/cc note: Specific Gravity of Jacobsite =4.75 gm/cc.
Fermion Index:
Fermion Index = 0.01 Boson Index = 0.99
Photoelectric:
PEJacobsite = 20.56 barns/electron U=PEJacobsite x rElectron Density= 92.33 barns/cc.
Radioactivity:
GRapi = 0 (Gamma Ray American Petroleum Institute Units) Jacobsite is Not Radioactive
Chemical Formula: 
