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;
- 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.
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.