Which one of the following is not a property of pure quartz?

Quartz is one of the most abundant and well-known minerals on Earth, composed chemically of silicon dioxide (SiO₂). It occurs naturally in igneous, metamorphic, and sedimentary rocks and forms hexagonal crystals. The term “pure quartz” refers to quartz that is free from any impurities or inclusions of other elements.

In its pure form, quartz is colorless and transparent. This is because pure silicon dioxide lacks any metal ions or impurities that could alter its color. The color variations seen in natural quartz varieties—such as amethyst (purple), rose quartz (pink), or smoky quartz (brown)—arise from the presence of trace elements or radiation effects. Therefore, the description “coloured solid” does not apply to pure quartz.

In contrast, quartz is known for its hardness and brittleness. It ranks 7 on the Mohs scale of hardness, meaning it can scratch glass and most metals but can be scratched by topaz, corundum, or diamond. This hardness makes quartz a common component in sandpaper and abrasives, but despite its hardness, it is brittle, meaning it can fracture rather than bend when struck.

Quartz also exhibits high chemical resistance and does not easily react with acids (except hydrofluoric acid). It is insoluble in water and melts at around 1,710°C, which shows its strong silicon-oxygen bonding network.

Due to these properties, quartz is used in glass manufacturing, electronics (as oscillators and resonators), optical instruments, and construction materials. However, only colored varieties of quartz (due to impurities) display different shades, while pure quartz remains colorless.

Hence, the statement “coloured solid” is not a property of pure quartz, making option A the correct answer.