2.8 Sand, sandstone and quartzite
The glass in the screen of your phone is made of silicon, just like the silicon found in the chips that make it run. In the chips, it is in its purest form as silicon, whereas in glass, it is silicon dioxide, SiO2, which geologists refer to as silica. Besides your phone screen, silica also makes up the glass that’s all around us. But where does it come from?
Silicon dioxide is quartz – a very common, grey/translucent rock-forming mineral in igneous and metamorphic rocks. It’s also very hard.
Just like with the other ores, we use geological processes to do a lot of the work of purifying the silica for us. Because quartz is very hard, when a lot of rocks are weathered and broken down into their constituent parts, quartz tends to survive the longest. This hardness also means that it can be transported by water and wind, without breaking down into very small pieces or being dissolved and going into solution.
So if you start with a rock that has lots of different minerals in it, weather it, and transport the bits, quartz tends to be the mineral that you end up with. This is why beaches are so often made of quartz sand – the power of the waves breaks down everything that isn’t quartz and takes it away, doing a great job of purifying the quartz.