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Quartz is a very common type of mineral. You may hear other names when it has colors or looks different. Agate, Amethyst, Rose quartz are some names for quartz. It is a semi-precious gemstone. Quartz is a component used to make quartz clocks. Sand often has a lot of small quartz bits. This mineral contains silica. Quartz has a mineral hardness of 8. (mohs scale).
The word "quartz" comes from the German word "quarz". It also came from "twark", which came from Slavic (cf. Czech tvrdy ("hard"), Polish twardy ("hard"), Russian твёрдый ("hard")), from Old Church Slavonic тврьдъ ("firm"), and from Proto-Slavic *tvьrdъ. 
Quartz can be useful in many ways, for example in TV and clock screens, jewelry and glass. Quartz crystals can often be found in mountains and high-altitude areas.
- http://www.etymonline.com/index.php?term=quartz etymonline.com