Dolomite tors: Harboro' Rocks
Large areas of the south-eastern part of the limestone plateau have been altered to dolomite, a rock made of the double carbonate of calcium and magnesium . Dolomite tends to be more porous and weathers more easily than unaltered limestone. This results in the prominent crags or 'tors' that are a conspicuous feature of the dolomite landscape.
The distinctive buff-brown coloured, porous dolomite is well seen in the castellated escarpment of Harboro' Rocks which is popular with rock climbers.
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The cause of the alteration of limestone to dolomite, and the source of the magnesium required is uncertain, but may be part of the process of mineralisation (see Metals and mines) which has occured elsewhere in the area.
Dolomite has numerous uses, chiefly as a raw material for glassmaking and in the steel industry. However, most of the dolomite in the Wirksworth-Brassington area is of low chemical quality and the numerous small, disused quarries marking the dolomite outcrop mostly produced material for use as low-grade roadstone. At a few sites, the dolomite is of higher purity and between 1963 and 1968, it was used to manufacture magnesium metal.
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