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Hardness

Quartz Quartz

Hardness: 7
Colour: White and colourless are by far the most common forms, but it can also be purple (amethyst), pink (rose quartz), or brown to black (smoky quartz)
Streak: White
Lustre:Crystals are usually vitreous
Other characteristics: Crystals are often found in the shape of a hexagonal prism, with a six sided pyramid 'peak'

Gemstone quality: It is hard enough to be cut and used commonly in jewellery. Amethyst, rose quartz and citrine are often used in pendants and earrings, but it is not a very valuable stone.
Industrial uses: It is the main ingredient of glass and is also used in components of computers, watches and clocks.

Drinking glass Silicon chips Wrist watch

Quartz is used to make glass and silicon chips in computers. The timing in watches is often controlled by quartz pieces.

Return to Mohs scale to learn more about hardness.