Then someone had an idea: what about digging even deeper into the Zechstein Sea? They pulled out the old rock cores from those first surveys back in the 1930s. Beneath the layers of sylvite was a layer of something never before discovered in such vast quantities: polyhalite, a hard, stony crystal of sulphur, magnesium and calcium whose name quite literally means “many salts.” Could they mine that? So as they searched for a rationale to keep the mine alive, the team at Boulby pondered the ingredients in polyhalite: sulphur, magnesium and calcium.
