Rock salt is a natural product, found underground where the remains of ancient dried-up salt water seas have formed into salt crystals which are accessible only by mining. Mining grit salt is very different to the traditional image of cramped dark areas and men with pickaxes. The nature of grit salt mines mean they resemble vast caverns, up to 20 metres wide. Rock (grit) salt remains the most commonly used method of removing ice and snow from the ground. All kinds of salt are effective at breaking up ice crystals, but grit salt is the preferred method for use in salt-spreading machines as long as the grit salt is kept dry. The grit salt also adds some friction to flat areas, making the ground better for tyres and shoes to grip onto