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General Information:
 Chemical Formula:
Fe++Al2O4
 Composition:
(Molecular Weight = 173.81 gm)
Aluminum 31.05 % Al
Iron 32.13 % Fe
Oxygen 36.82 % O 
 Empirical Formula:
Fe2+Al2O4
 Environment:
Magmatic.
 Locality:
Pobezovice, Czechoslovakia.
 Name Origin:
From the old Latin, Hercynia Silva, "Forested Mountains."
Physical Properties:
 Cleavage:
[111] Indistinct, [111] Indistinct, [111] Indistinct
 Color:
black.
 Density:
3.95
 Diaphaniety:
Opaque
 Habits:
Euhedral Crystals - Occurs as well-formed crystals showing good external form., Massive - Granular - Common texture observed in granite and other igneous rock., Granular - Generally o ccurs as anhedral to subhedral crystals
 Hardness:
7.5 - Garnet
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
dark green
More details...

See more at Wikipedia.org...

General Information:
 Chemical Formula:
Fe++Al2O4
 Composition:
(Molecular Weight = 173.81 gm)
Aluminum 31.05 % Al
Iron 32.13 % Fe
Oxygen 36.82 % O 
 Empirical Formula:
Fe2+Al2O4
 Environment:
Magmatic.
 Locality:
Pobezovice, Czechoslovakia.
 Name Origin:
From the old Latin, Hercynia Silva, "Forested Mountains."
Physical Properties:
 Cleavage:
[111] Indistinct, [111] Indistinct, [111] Indistinct
 Color:
black.
 Density:
3.95
 Diaphaniety:
Opaque
 Habits:
Euhedral Crystals - Occurs as well-formed crystals showing good external form., Massive - Granular - Common texture observed in granite and other igneous rock., Granular - Generally o ccurs as anhedral to subhedral crystals
 Hardness:
7.5 - Garnet
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
dark green
More details...