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.

Also read:

• Calcium Minerals
• Polymorphs (Al2SiO5 Minerals)
• Minerals of Clay group
• Minerals of Serpentine group