• Question: Why can we find different colours of sand?

    Asked by anon-244767 on 30 Apr 2020.
    • Photo: Kerrianne Harrington

      Kerrianne Harrington answered on 30 Apr 2020:

      Sand is very finely broken up material. It is made up of lots of different rocks and minerals slowly broken down by the sea. So the colour will change based on the local material. The most common thing that makes up sand is silica – which is really important in my job for making the glass we use for optical fibres.

    • Photo: anon

      anon answered on 30 Apr 2020:

      Sand is generally made out of rocks ground to tiny particles, so the colour depends on what it is made of. Volcanic rocks are very dark for instance. There can also be organic matter, like bones, seashells, fossils. Have a look at sand through a big lens or a microscope – it’s very cool.

    • Photo: Malgorzata Drwila

      Malgorzata Drwila answered on 30 Apr 2020:

      Sand can be formed from almost any type of rock, and rocks have different colours. Most of the sand is made of quartz mineral (silica), because quartz is very common and it’s harder than most of the common minerals. It means that quartz particles can travel big distances long after other minerals got totally destroyed. Smaller particles of quartz are lighter so they can travel further. Quartz is usually bright and quite transparent.

      Some of other examples are black sands of Hawaii or Iceland beaches. There the sand is made during weathering process of the basalt rock, which is a black igneous rock, which comes out of volcanoes (and there are many volcanoes in Hawaii and Iceland).

      There are some deserts full of very white sand, which comes from gypsum rock.

      Some sand can even be produced by animals! Check out this explanation of Maldives sand formation:
      https://www.scientificamerican.com/video/parrot-fish-poop-makes-beautiful-beaches/

    • Photo: Lisa Hollands

      Lisa Hollands answered on 30 Apr 2020: last edited 30 Apr 2020 12:16 pm

      Sand is actually made up from from rocks surrounding the area that is is found that have been broken up over time. If you have a look at the sand on a beach closely, you can often see that it is not just 1 colour but lots showing that it is made up from lots of different types of rocks.

      The sand that I use in my glassmaking is actually 1 type of mineral only and that is silica. I tend to use very pure silica to make my glass as colourless as possible. As the purity of the silica sand reduces and other elements start to be seen then we start getting a small amount of colour in the resulting glass – i.e. only a tiny bit of iron in the silica sand can produce a glass with a very slight green tint. The colour of a pure silica sand is off white/ pale beige – as the amount of iron increase, the silica sand starts to look browner.

    • Photo: Susan Cartwright

      Susan Cartwright answered on 30 Apr 2020:

      I don’t have much to add to other answers. Sand is finely ground material, and the colour of the sand is determined by the colour of the original material. The most well-known unusually coloured sands are the black sands of many volcanic islands, produced by grinding up basalt, which is a very dark rock. Some types of limestone are almost entirely made of fossilised shells, and sand made from these is very nearly white. As someone said, it is well worth looking at some sand grains under a microscope!

    • Photo: Greg Wallace

      Greg Wallace answered on 1 May 2020:

      small addition to the other answers: the white sand you see in topical islands usually comes from smashed up coral as these islands tend to be surrounded by reefs. waves ocasionally break off bits of coral from the reef and these then get pounded into sand by the waves moving them against other bits of sand and coral. If you walk along these beeches you can occasionally see larger bits of coral.
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      you can also get red sand on some beaches which result from there being lots of iron in the rocks that make the sand
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      So in conclusion: yellow sand from your standard silica rocks, black sand from volcanic rocks like basalt, white sand from some white sedimentary rocks or coral, and red sand from rocks with lots of iron in them.

    • Photo: Paula Koelemeijer

      Paula Koelemeijer answered on 1 May 2020:

      Did you know, that the colour of sand can also change? This is because different minerals are more stable than others. So when we start with a mixture of colours in sand high up in the mountains, some of the less stable minerals will dissolve and weather away, while quartz (the most stable mineral) remains. When you go follow a river down from the mountains to the sea, the colours of the pebbles and rocks therefore tend to become more the same!

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