Alluminium Minerals

The minerals which contain aluminium element are known as the Aluminium Minerals. Some of the important aluminium minerals are as under:

(1). Bauxite: Al2O3

Bauxite is a mixture of hydrous aluminium oxides. The physical properties of Bauxite are as under;

Physical Properties:

  • Crystal System: Bauxite is a mixture of several minerals such as gibbsite,diaspore, and boehmite.
  • Cleavage: Non-cleavage mineral
  • Fracture: Uneaven
  • Hardness: 2-2.5
  • Lustre: Dull earthy lustre
  • Colours: White, gray, yellow, or brown.
  • Steak: Bauxite gives yellow and brown streak on streak plate.
  • Habit: Pesolite and massive

Occurrence of Bauxite:

Bauxite is a secondary product, commonly formed under subtropical to tropical climatic conditions by the leaching away of silica from aluminium-bearing rocks.

Uses of Bauxite: 

  • As Bauxite is an important ore mineral of aluminium, therefore, it is used as a major source of aluminium.
  • Bauxite is used as an abrasive material.
  • It is also used in refractory industries.
  • Bauxite is used in the manufacturing of high alumina cement.
  • Also used as a catalyst by the oil industry.
  • Bauxite is used as a flux in making steel and ferroalloys.
  • Bauxite is used to coat the welding rods.

(2). Corundum: Al2O3

Corundum is a rock-forming mineral, which typically contains traces of iron, vanadium, titanium and chromium. The inclusion of these materials makes Corundum very hard.

Physical properties of Corundum:

  • Crystal System: Hexagonal crystal form.
  • Cleavage: Corundum has no cleavage.
  • Fracture: Corundum is broken into uneven fractures.
  • Hardness: 9 in Moh’s scale.
  • Sp.Gr.: 4.02.
  • Lustre: Corundum has vitreous to adamentine lustre.
  • Colours: Corumdum is found in bluish and gray colours. Gem Varieties are transparent to translucent. Ruby is of red colour, and ‘sapphire” is of blue colour.
  • Habit: Commonly found in tabular crystals, also massive or granular.

Occurrence: 

Corundum is found in some metamorphic rocks, such as mica-schist and gneiss. It is also found in igneous rocks like pegmatites and some nepheline syenites. Gemstones are found in placer deposits.

Uses of Corundum: 

  • Corundum is used as a precious gemstone.
  • Like bauxite, the corundum is also used as an abrasive material.
  • Being extremely hard (9 on Moh’s scale) it is used to cut and abrade glass, and grinding and polishing optical glasses and metals. Therefore, it is used in making sand-papers and grinding wheels.

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