This is the mineral Quartz. It has a specific gravity of 2.6 and a vitreous luster. Vitreous simply means that quartz often looks like glass. Its white streak contrasts well against a black ceramic streak plate. Quartz is composed of the two elements Silicon and Oxygen, and thus belongs to the Silicate chemical family. Note that Oxygen and Silicon are the two most abundant elements in Earth’s crust, thereby making quartz a very common mineral. It ranks 7 on Mohs hardness scale, which is quite hard compared to other minerals. It does not exhibit cleavage, but when fractured often produces sharp, angular, and irregular surfaces. Sometimes quartz exhibits a conchoidal fracture, which looks like the smooth and concave undulations of a seashell. Quartz naturally occurs in many different varieties, and often contains elements that create unique colors and textures. For example, you may have heard of Jasper, Flint, Tiger’s Eye, Amethyst, Citrine, and Agate. These are all quartz varieties. You also may have heard of Rose Quartz, which looks pink, or Milky Quartz, which looks cloudy and white. We use quartz every day. For example, if you’ve ever looked through a window, you’ve looked through quartz because it’s one of the three primary ingredients of glass. It's also a useful sandblasting and abrasive agent. Some of the world’s most beautiful beaches are composed of Silica sand, which is just very small quartz fragments. Piezoelectricity is one of the more fascinating and useful characteristics of this mineral. Under mechanical stress it produces an electric charge, and conversely, when an electric charge is applied, it vibrates at a predictable frequency. This is why it’s used in timekeeping, and why the word Quartz often appears on watch faces.