Last month I wrote about the marvels of the beautiful golden stuff that makes up our beaches. Ah, but it’s not always golden as beaches come in a wide range of colours.
Hyams Beach in Jervis Bay claims to be the whitest sand beach in the world, but Whitehaven Beach in the Whitsundays makes the same claim as do many other beaches around the world.
How white is white? In the case of Hyams, the sand is extremely old and was deposited in the region during higher sea levels about 120,000 years ago. Over that time all the impurities of the sand grains have been abraded away leaving behind almost pure quartz crystals and a ton of Instagrammers seeking a selfie.
Locally, beaches like Stanwell Park or Thirroul contain quartz sand that is a little younger and still coated with material giving it a browner colour.
Then there’s the multi-coloured sands of Rainbow Beach in Queensland, which supposedly contain 72 different shades of colours.
The different colours are all related to the amount of iron contained within the ancient river deposited sand found in the beach and dunes. As iron oxidises (or essentially rusts) it creates various hues of reds, oranges, pinks and yellows. The more iron present and the longer the oxidation process has been going on, the redder the sand gets.
Black sand is volcanic in origin which is why you only get well-developed black sand beaches in places like New Zealand, Hawaii and Iceland. The source rock is also different and, instead of quartz minerals, you get sand grains made up of heavy minerals (which are black) like zircon and rutile.
Hawaii also has green sand beaches, which at first appear to be growing a layer of mould. The green sands are also volcanic in origin and form under special conditions where molten lava cools very quickly when it enters the ocean. This creates olivine minerals, which are green in colour.
If you ever travel to a coral reef island, the sand is often a beautiful white, but it’s not quartz grains, it’s almost entirely made up of calcium carbonate sediments derived from coralline algae and broken bits of coral from the surrounding reefs.
Do your research before you head to a tropical island as the beaches are not always made of nice, powdery white stuff. More often it’s made up of rough and jagged bits of coral that can make mince-meat of your bare feet.
Finally, there’s Shell Beach in Shark Bay, Western Australia, which is completely made of small shells, that become so sticky that the public toilet is made of blocks cut out from the beach. Impressive stuff!
Have a question? Email rbrander@unsw.edu.au