Captivating sand
The tide has turned and is on its way in. The children run on ahead of me in their pants, down the beach and out across wet sand to distant surf. The sea is turquoise inshore and deep blue to the horizon; in the shallows, with the cross-shore breeze, the Atlantic waves collapse into foaming white water.
Although the children are way out now they are barely waist-deep, and as each wave crumbles around them they jump and are swallowed, disappearing briefly before re-emerging, exhilarated, nearby – now and then clutching their pants.
I roll up my jeans and wade out into the shallows with my camera. Unlike further out, the waves here are gentle, running in over sun-warmed sand. Ankle-deep the water is delicious. Now and then, in a rush of new cold, a wave rises around my calves and then retreats, not mixing at first but leaving fingers of warmth in its wake.
After weeks of quiet summer weather the water is clear as glass. Below, refracted by its lens-like surface, sunlight ripples in waves across the seabed sand. Where the water is shallowest – over gentle banks and ridges – tiny glassy waves form, lining up to chase each other in. I follow them through the camera’s lens but they are fleeting, already vanishing and never quite repeated. The tide moves on, taking with it its patterns of light; where I stood ten minutes ago is already taken back by the sea.
As always, through the slight close-up of the lens, the sand’s seemingly uniform golden-tan reveals itself to be an extraordinary variety of colours, and the closer I look, the more I see. To go further and view it through a microscope gives some idea of the true beauty and variety of sand, and perhaps something of the story each of these grains has to tell.
There are two types of grain that make up sand. Mineral sand is formed from rocks through a process of erosion, and biogenic grains are the remains of once-living organisms. By far the majority of sand comes from granite, a hard, resistant rock that breaks down into grains of quartz, feldspar and hornblende, along with the shiny flakes of mica that can give sand its glitter. Some of the most striking mineral grains are tiny gemstones – such as garnet, topaz or amethyst – their crystal forms ground and polished by the waves.
A grain’s roundedness gives an indication of its age, and possibly how far it has travelled. A smooth, well-rounded grain of quartz may well have broken away from its parent rock hundreds of millions of years ago, and may have survived repeated cycles of erosion and compression, for example into sandstone. Angular mineral grains are likely to be younger and often more local.
Under the microscope, the most sculptural and beautiful of the sand grains are biogenic: minute, waveworn fragments of the shells and skeletons of creatures both familiar and strange. I have a copy of the book A Grain of Sand by Gary Greenberg and his photographs of those biogenic grains taken through a powerful microscope, are captivating.
Some of my favourites are from sea urchins. There are minute remnants of baby urchin shell, delicately coloured and patterned with circles, worn so thin they are now translucent. The fragments of urchin spines are intricate green or purple rods, often beautifully rounded, and running through the centre of each – like a stick of rock – is a perfect mandala. There are also remnants of corals, grain-sized pieces of mother-of-pearl, and the
Some mineral grains are tiny gemstones: garnet, topaz or amethyst
beautifully eroded fragments of tiny shells, with just the seaworn traces of their original forms: spirals perhaps, or radial ribs and grooves. I also love the sponge spicules: glossy, needle-like structures that give sponges their shape and strength. Often three, four or five-pronged, they can also be shaped like fish-hooks or hairpins, spiders, even anchors and are how scientists confirm a sponge’s species.
For me though, the best sand grains are the foraminifera, which means ‘hole-bearers’. These were once the intricate shell-houses of microscopic creatures that live either in the plankton or on the seafloor. There are thousands of species, both living and extinct, and whilst their chalky skeletons appear fragile, incredibly many survive the ravages of the waves and abrasion of the sand in almost perfect condition. Under a microscope they are often beautifully rounded, their wave-polished forms at times with the texture of porcelain.
The sand here, shifting beneath my feet with the swash and backwash of the waves, is for me – without a microscope or an expert to hand – a mystery. There are quartz grains, definitely, and mica, and the black flecks are probably magnetite – it turns out you can check this with a magnet. There will no doubt be slate from local bedrock, and possibly grains of greenstone or serpentine, carried by the tide from further west.
There may also be brilliantly coloured gemstones. Agate, topaz, jasper, opal and amethyst are all found in Cornwall, even tiny amounts of gold. There will be grain-sized fragments from the skeletons of the creatures that live in these waters: the sea urchins and sponges, sea mats and starfish, and the hundreds of species of mollusc, lobster and crab. There will also be beautiful foraminifera.
For someone who can read it, a handful of this sand can provide a fascinating geological and biological history of this whole stretch of coast.
After half an hour the children are out of the sea, skinny and freezing, running over to a series of shallow pools in the sand. The water here, in depressions left by the tide, has lain all day in the sun and is warm as bathwater. They lie in them, low as they can for the warmth, wriggling their bodies down into the sand like flatfish.