I don’t think we appreciate beach sand as much as we should. This thought went through my mind years ago while walking across the black sand on New Zealand’s Piha Beach.
It was a sunny day and the sand felt nice and warm. Hot, even. In fact, boiling hot to the point of having to sprint to the water to cool off my burning feet.
Trapped, I looked around at others doing the same thing, standing in the shallows, marooned on towels on the beach, and standing on meagre vegetation in the dunes for relief as they tried to escape the inferno of the black sand. So, perhaps we shouldn’t take beach sand for granted.
If you pick up a handful of sand, it’s full of thousands of sand grains of different sizes, colours and origins that all have a story to tell because beaches are essentially dumping grounds for the end products of millions of years of erosion of the earth’s surface.
On beaches in New South Wales, the vast majority of grains in that handful will be quartz minerals. That’s because the most common type of rock on the earth’s surface is granite, which just happens to be made up of mostly quartz minerals that are exceptionally hard and resistant.
Most beach sand tends to be lighter in colour because pure quartz crystals are white. Generally the older the sand is, the more white it is, as all the material and staining that coats the grains gets worn off over time. Sand with a reddish tinge, tends to have a bit of iron staining around the quartz grain.
Although not on the scale of some New Zealand beaches, you will likely see a few black sand grains in the handful you picked up and these are completely different, being volcanic in origin and are derived from basalt rocks (old lava flows) and, yes, Australia has had plenty of volcanic activity in the past.
Black sand is made up of heavy minerals, such as zircon and rutile, which actually have industrial value and are mined commercially. Because they are heavier, they work themselves down through the sand and tend to concentrate, becoming exposed as black streaks on a beach after large waves have eroded the sand on top offshore.
Finally, you’ll probably find a small amount of broken bits of shells in your handful, giving it a bit more colour and coarser texture. Any beach that has extensive rock platform environments, which are perfect habitats for animals that live in shells, will have a fair amount of shell (calcium carbonate) content.
So, there’s a lot more to sand than you might think … so much more that I think I’ll have to continue this topic next month!
Have a question? Email rbrander@unsw.edu.au