- Quartz-dolerite
An
intrusive rock, similar todolerite , but with an excess ofquartz .Dolerite is similar in composition tobasalt , which is eruptive (fromvolcano es), andgabbro , which isplutonic . The differing crystal sizes are due to the different rate of cooling,basalt cools quickly and has a very fine structure, whilegabbro cools very slowly, at great depth, and large crystals develop.Dolerite is intermediate.Quartz-dolerite is very common in central
Scotland , in intrusive formations,sill s and dykes, and is widely quarried for roadstone. It was used with some success for making millstones at one time, themillstone grit part of thecarboniferous strata not being present inScotland , but it is no longer used for this purpose, and would probably be illegal now due to the formation of smallquartz and othersilicate particles, which could cause the serious respiratory diseasesilicosis .In
Scotland quartz-dolerite is commonly known as whin or whinstone.Quartz-dolerite contains many cooling fractures and weathers badly, becoming unstable. It is not uncommon for large boulders to break loose, and significant rockfalls are not uncommon. It is regarded as dangerous as far as climbing is concerned.
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