This article belongs to a series called MarvelousMonday. On some mondays I share a few noteworthy scientific facts about a specific mineral with you. I've assembled a glossary in case you need a little more background information on the terminology regarding minerals & crystals (click here).
This week's mineral: Quartz
Quartz is of white or greyish color, but can also appear transparent/translucent or in other colors (see varieties). It's a very important rock-forming mineral and a very abundant mineral in the Earth's crust. It's composed of only two elements: silicon and oxygen (silicon dioxide, chemical formula: SiO2).
Quartz (alpha-quartz) belongs to the trigonal crystal system and can have many shapes and habits. Oftentimes, many crystals are bulged and intergrown with other quartz crystals and other minerals, which makes it hard to identify the crystal system at first look.
Despite these few simple ingredients (silicon dioxide) quartz has an array of modifications and varieties.
Depending on pressure and temperature, different modifications of quartz form.
The term quartz (to be precise: low quartz or alpha-quartz) actually only describes the low-pressure, low-temperature modification that is stable under 573°C. When pressure and/or temperature increase (e.g. deeper in Earth's crust) low-quartz is modified into: high quartz (or beta-quartz), tridymite, cristobalite, coesite or stishovite. These processes are very complicated.
There exist many varieties of quartz: amethyst, rose quartz, milk quartz, smoky quartz, berg quartz, agate, jasper, chalcedony, citrine, and others.
Perhaps you've heard of these varieties before but up until now thought they were separate minerals. In fact, they have the same chemical composition (SiO2), but differ in colour. Where these colours come from I'll explain next monday!
If broken apart or fractured, quartz displays a conchoidal pattern. This is very characteristic, as other minerals may display smooth cleavage or other fracture patterns. You see, in mineralogy fracture doesn't equal fracture!
Another striking feature is their hardness. Quartz is a reference mineral on the Mohs Scale (a scale which helps to define the hardness of a mineral) and has a hardness of 7 (out of 10). This means it can scratch f.e. glass and teeth!
If you've ever been to a beach (you most probably have) then you've likely walked on quartz! Some sandy beaches are mostly composed of tiny quartz fragments.
Quartz is very versatile in use and of high importance in the manufacturing industry worldwide. It is used to produce glass, cement, porcellain and other ceramics.
High-purity quartz is very valuable for the high-tech industry, as it is used for manufacturing crucibles used to grow single crystals of silicon. Those are needed for solar panel and micro-chip production. Quartz is also of high importance in the telecommunications and semiconductor manufacturing industries.
Quartz crystals exhibit piezoelectricity. This means that quartz crystals polarize (they get electrically charged on their surface) as a reaction to mechanical pressure. On the other hand, it'll strech and compress ("squeezes") by vibrating if electricity (voltage) is applied, causing the quartz crystal to oscillate. Therefore, quartz crystals are used as quartz oscillators in clocks or watches, microphones and many other instruments.
And last but not least: Quartz is a popular gemstone and used in jewelry making.
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Mineralogy of Quartz and Silica Minerals, Edited by Jens Götze (www.mdpi.com/journal/minerals)
Quartzpage.de: Physical Properties
Mineralienatlas.de: Quartz (retrieved: March 29th, 2020)
Borchardt-Ott, Walter und Sowa, Heidrun (2018): Kristallographie, Eine Einführung für Studierende der Naturwissenschaften. 9- Aufl. Springer Spektrum. Berling Heidelberg 2018.
Chemie.de: Piezoelektrizität (retrieved: March 29th, 2020)
Markl, Gregor (2015): Minerale und Gesteine, Mineralogie - Petrologie - Geochemie. 3. Aufl. Springer Spektrum. Berlin Heidelberg 2015. S.161 ff.
Didier Descouens. Quartz, Location: Minas Gerais, Brasil. Licensed under Creative Commons Attribution-Share Alike 4.0 International