The physical properties of quartz, corundum, haematite, mag chromite, bauxite, graphite, calcite, magnesite, orthoclase, microcline, plagi biotite, muscovite, olivine, topaz, talc, granet, beryl, hornblende, augite, silli kyanite, pyrite, chalcopyrite, gypsum, apatite and fluorite are described below.

Quartz:

Chemical composition: Quartz is composed of silica and oxygen, in purest form it is silicon dioxide (Si02; Si = 30.5% and O = 69.5%)) colorless (rock crystal) or white in colour. Substitution of Al+3 for Si+4 results in introduction of Li+1, Na+1, Ti+2 etc, which impart different colours to quartz. This substitution, however, takes place in very minor quantities (0.0001 – 0.0216 %).

Physical properties:

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(i) Form: Massive and crystalline are common forms. Rock crystal (transparent variety of quartz) is crystallized with well-developed crystal faces. Chalcedony is fibrous microcrystalline.

(ii) Colour:

Pure quartz is colourless. Different varieties of quartz are differently coloured. Rock crystal is transparent, citrine is yellow, amethyst is purple, rose quartz is pink, smoky quartz is yellow-brov/n to black, morion is black, milky quartz is milky white, carnelian is red, sard is brown, chrysoprase is apple green, agate is banded or variegated, onyx is white with gray bands, jasper is iron red, chert is light gray, flint is dark coloured.

(iii) Lustre: Vitreous to sub-vitreous.

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(iv) Streak: White.

(v) Hardness: 7.

(vi) Cleavage: Absent.

(vii) Fracture: Commonly conchoidal, even in case of chert.

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(viii) Specific gravity: 2.65.

(ix) Diaphaneity: Transparent (rock crystal) to translucent.

(x) Special property: Piezoelectric.

Use:

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Quartz is used in building industry (sand), glass making, abrasive in soap and toothpaste industries, pottery, in preparation of silica bricks (refractory) and manufacture of ferro-silicon. It is also used as a flux, as
lining of tube-mills (grinding of ores and minerals) and as a filler! Its piezoelectric property, quartz is extensively used in short waveij apparatus and radio circuits.

Thin quartz plates, which functioi oscillators and mechanically vibrate at a constant rate, are usi electronic circuit in the watch. This circuit counts the crystal freque and provides digital time display of the watch. It is also manufacture of quartz-wedge, used in petrological microscopes.