Oxides and Hydroxides: Magnetite

Composition: Fe₃O₄; calcium, magnesium and manganese may substitute for ferrous iron (Fe₂) and aluminium, titanium, vanadium and chromium may substitute for ferric iron (Fe₃)

4.9.1
banded iron formation
WA Australia

Crystal system: Isometric; crystals commonly octahedral, also massive

Properties:

• Metallic lustre
• Black color
• Black streak
• Knife will not scratch or barely scratches (Mohs Hardness 5.5-6.5)
• High density
• No cleavage
• Smooth fracture or parting
• Strongly ferromagnetic
• Dissolves slowly in hydrochloric acid (HCl)
  

Occurrence:

Magnetite is one of the most common oxide minerals. It occurs as an accessory mineral in igneous and metamorphic rocks, with other oxides in massive segregations in mafic igneous rocks, with sulfides in hydrothermal ore deposits and in heavy mineral sand deposits .

4.9.2 magnetite with calcite Biggenden mine Qld Australia	4.9.3 magnetite with calcite Biggenden mine Qld Australia

4.9.4 magnetite crystals	4.9.5 magnetite crystals

4.9.6
banded iron formation
WA Australia

Magnetite is an important source of iron; vanadium is also recovered from vanadium-bearing magnetite.