Short notes on the Chemical composition, Physical properties and uses of Bauxite


Chemical composition: Bauxite is a mixture of three aluminium hydroxide mineral phase’s viz.

diaspore (HAIOJ, gibbsite [Al (OH),] and bohemite [AIO (OH)] in different amounts. Common impurities are Fe203, TiO^ and phosphorus compounds.

Physical properties:


(i) Form: Amorphous, earthy granular or pisolitic masses.

(ii) Colour: Dirty white, grayish, brown, yellow or reddish brown.

(iii) Lustre: Earthy.

(iv) Streak: Dirty white to brown.


(v) Hardness: 2 -3.

(vi) Cleavage: Absent.

(vii) Fracture: Conchoidal.

(viii) Specific gravity: 3-5.


(ix) Diaphaneity: Opaque


Bauxite is used for extraction of aluminium metal, preparatii refractory bricks and manufacture of A1, 03, which is used as abrasive

Chemical composition: Graphite is composed of pure carbon. Cora impurities are Si02, FeO and clay minerals.


Physical properties:

(i) Form: Foliated, scaly, lamellar, columnar, radiating or gri aggregates. Crystalised form is hexagonal tablet.

(ii) Colour: Iron gray to deep steel gray.

(iii) Lustre: Metallic.


(iv) Streak: Shining black.

(v) Hardness: 1 – 2 (marks paper).

(vi) Cleavage: One set perfect basal.

(vii) Fracture: Conchoidal to uneven.

(viii) Specific gravity: 2 – 2.3.

(ix) Diaphaneity: Opaque

(x) Feel: Greasy

(xi) Tenacity: Sectile, flexible

(xii) Electric property: Good conductor of electricity.

Use: Graphite is used in manufacture of refractory crucibles, batteries, paint, and lead of pencil. It is also used as electrodes in electric furnaces and as generator brush, lubricant and in electro-plating.

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