Quartz dolerite or quartz diabase is an
intrusive rock
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: Marc ...
similar to
dolerite
Diabase (), also called dolerite () or microgabbro,
is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...
(also called diabase), but with an excess of
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
. Dolerite is similar in composition to
basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...
, which is
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates ...
, and
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
, which is
plutonic
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
. The differing crystal sizes are due to the different rate of cooling, basalt cools quickly and has a very fine structure, while gabbro cools very slowly, at great depth, and large crystals develop. Dolerite is intermediate.
Quartz dolerite is very common in central
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...
, in intrusive formations,
sills and
dykes, and is widely quarried for roadstone. It was used with some success for making millstones at one time, the
Millstone Grit part of the
carboniferous strata not being present in Scotland, but it is no longer used for this purpose, and would probably be illegal now due to the formation of small quartz and other
silicate particles, which could cause the serious respiratory disease
silicosis
Silicosis is a form of occupational lung disease caused by inhalation of crystalline silica dust. It is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis. Silicosi ...
.
In Scotland, quartz dolerite is commonly known as whin or whinstone.
Quartz dolerite contains many cooling fractures and weathers readily, 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.
Mafic rocks
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