Sand

Sand is loose rock debris with grains roughly 0.06 to 2 millimetres across. In other words, “sand” is the name of a grain size, not of a mineral. As rocks weather and crumble, soft minerals turn into clay or dissolve, while hard, chemically resistant quartz is left behind. That is why the sand of continents and temperate coasts is mostly quartz. The white sand of tropical beaches is made of coral and shell fragments, and the black sand of volcanic islands of basalt or magnetite. Sand is the raw material of concrete, glass and silicon chips; compacted and cemented, it becomes sandstone.

Concrete and mortar: Together with gravel and cement, sand is a main ingredient of concrete, and it is also used in plaster and mortar. The best sand for concrete is angular, clean river or pit sand. Glass: Silica-rich sand is the main raw material of ordinary glass. Silicon: The silicon used in solar panels and electronic chips is made from pure quartz sand. Casting, filters and blasting: It is used in moulds for metal casting, in drinking-water filters and for surface cleaning. Coasts and land: It is used to replenish beaches and to build up reclaimed land.

You can see the individual grains with the naked eye and they feel gritty between your fingers. Silt and clay are too fine to see grain by grain and feel smooth like flour or dough. Under a magnifying glass, glassy, colourless or milky grains are usually quartz. White, opaque grains that look like broken shell are calcium carbonate and fizz when a drop of vinegar is added. Test black grains with a magnet: those that stick are magnetite. Black grains that do not stick are mostly fragments of basalt or volcanic glass. Most coloured sands sold for aquariums and decoration are dyed quartz sand or crushed glass, not naturally coloured.

On the “street to diamond” value ladder it sits on step 1 of nine: Everywhere, worthless. Sand is one of the cheapest raw materials, sold by the tonne, and transport makes up most of its cost. Building sand must have the right grading of grain sizes, be clean (free of clay, silt, organic matter and salt) and have angular grains. Glassmaking and silicon production need sand that is almost pure quartz with very little iron; silica sand of this quality is much rarer and more valuable.

When dry, fine quartz sand is cut, blasted or ground, it releases respirable crystalline silica dust; breathing it for long periods can cause silicosis. Quartz sand should be used for abrasive blasting only with proper protective equipment. Beach sand, by contrast, is harmless because it is not fine enough to be inhaled.