THE MINERAL MAGNETITE

• Chemical Formula: Fe3O4, Iron Oxide
• Class: Oxides and Hydroxides
• Group: Spinel
• Uses: Major ore of iron and as mineral specimens
• Specimens

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.

PHYSICAL CHARACTERISTICS:

• Color is black.
• Luster is metallic to dull.
• Transparency: Crystals are opaque.
• Crystal System is isometric; 4/m bar 3 2/m
• Crystal Habits are 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 is absent although octahedral parting can be seen on some specimens.
• Fracture is conchoidal.
• Hardness is 5.5 - 6.5
• Specific Gravity is 5.1+ (average for metallic minerals)
• Streak is black.
• Associated Minerals are talc and chlorite (schists), pyrite and hematite.
• Other Characteristics: Magnetism stronger in massive examples than in crystals, striations on crystal faces (not always seen).
• Notable Occurrences include South Africa, Germany, Russia and many locallities in the USA.
• Best Field Indicators are magnetism, crystal habit and streak.