Why should we care about quartz?

Quartz is beautiful. It shimmers in light and its rainbow of colors have stoked the imagination of everyone from admirers seeking spiritual healing to young geoscientists. But most quartz on Earth does not look like the gorgeous minerals we admire. Most of its forms are lackluster, dull and not translucent. But quartz plays important roles in the Critical Zone. So, why should anyone care about quartz in the Critical Zone?

Quartz is derived from East Central German, ‘quarz’, which roughly translates to ‘hard’. And as its name implies, quartz is hard! On the Mohs hardness scale, quartz is a 7 out of 10. This is harder than many natural and human-made materials like brick and glass, but it is not as hard as titanium or diamonds. The hardness of quartz is derived from its atomic mineral structure. Quartz is a framework silicate mineral, which are minerals composed of oxygen and silicon at a ratio of two oxygen per one silicon atom. The strength of the framework silicates is that oxygen and silicon atom are all connected in a network of strong bonds. This network structure is why quartz breaks with no clear planes of cleavage, called conchoidal fracture, like broken glass.

Although generally colorless due to its predominately silicon and oxygen composition, quartz can exist in a wide array of colors because of impurities. Amethyst (a purple quartz), rose quartz (pink), red quartz, and citrine (a pale yellow to brown quartz) owe their fabulous hues to impurities of iron, manganese, or titanium. Milky quartz gained its opaque characteristics from trapped gases and liquids. Smoky quartz can range from black to dark gray due to impurities of free silicon, not bonded to other oxygen and silicon.

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