Rocks and minerals
Pure quartz crystals are transparent, but the mineral is often found with traces of other minerals present. These minerals are very hard.
Because of their attractive appearance when polished, and their resistance to wear and corrosion, they are used as gemstones in jewellery.
Amethyst is a form of quartz that contains manganese and iron oxides. These give the gemstone its violet colour.
Many other giant covalent compounds are used in jewellery. The most famous is diamond.
The rarity of these minerals in the crust makes them very expensive.
Read on if you are taking the Higher paper.
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