Ontario Mineral - Magnetite

Rocks minerals Ontario Magnetite

Chemistry:

 Fe3O4, Iron Oxide

Class:

 Oxides and Hydroxides

Subclass:

  

Group:

 Spinel

Uses:

 Major ore of iron and as mineral specimens

Color:

 black

Luster:

 metallic to dull

Transparency:

 Crystals are opaque

Crystal System:

 isometric; 4/m bar 3 2/m

Crystal Habits:

 typically octahedrons but rarely rhombododecahedron and other isometric forms, most commonly found massive or granular. Twinning of octahedrons into spinel law twins is seen occassionally.

Cleavage:

absent although octahedral parting can be seen on some specimens

Fracture:

 conchoidal

Hardness:

 5.5 - 6.5

Specific Gravity:

 5.1+ (average for metallic minerals)

Streak

 black

Other Characteristics:

 Magnetism stronger in massive examples than in crystals, striations on crystal faces (not always seen)

Associated Minerals:

 talc and chlorite (schists), pyrite and hematite.

Local Occurance:

 Bessemer Mine, Burgess Corundum, Cancrinite Hill, Davis Hill, Lily Robertson

Best Field Indicators:

 magnetism, crystal habit and streak.

Description:

Magnetite is a natural magnet, hence the name, giving it a very nice distinguishing characteristic. Explaining the magnetism is not easy but here is a go at it. Remember, electricity produces magnetic fields just as magnetism produces electic fields. Magnetite is a member of the spinel group which has the standard formula A(B)2O4. The A and B represent usually different metal ions that occupy specific sites in the crystal structure. In the case of magnetite, Fe3O4, the A metal is Fe +2 and the B metal is Fe +3; two different metal ions in two specific sites. This arrangement causes a transfer of electrons between the different irons in a structured path or vector. This electric vector generates the magnetic field.