I’ve posted a couple of pictures lately showing water in the clay pits here in central Cornwall of the most surreal and vivid blue. Several people have asked the question, what makes the water this beautiful yet rather surreal blue/green/turquoise colour? I thought it must be down to minerals or chemicals left over from the clay workings. I was right in one sense, it is a mineral but not the copper I suspected.
I gave Imerys, the company that operates the china clay works, a call and spoke to Chris Varcoe. He told me the water in the bottom of the pits is a mixture of china clay, water and mica. Mica is what’s left over when the china clay, or kaolin is separated from the decaying granite rock using high pressure water. We’ve all seen mica, it’s what they use to make glitter and is a key ingredient used in the billion dollar beauty industry. Unfortunately that mica doesn’t come from the clay pits of central Cornwall, it’s a waste product here. The mica used in the cosmetics industry is largely mined in India, often by children.
Mica is a highly reflective mineral as we’ve all seen and when you mix it with china clay in suspension, it reflects light giving the water this vivid surreal colour. Water reflecting light is what makes the ocean blue, mix in some mica and a bit of china clay and the reflectiveness is greatly enhanced.
For those of you with a scientific bent, the mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having close to perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The almost perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms giving the mica its reflective properties.
It’s worth noting that this mixture of china clay in suspension and mica is a little like quicksand and extremely dangerous if you find yourself trying to swim in it hence the danger keep out signs and barbed wire fences everywhere. A timely reminder to an inquisitive photographer who might be tempted to get a little too close. ;-)