Dolerit

Dolerit, also spelled dolerite in English, is a term used in geology for a fine- to medium-grained mafic igneous rock that forms as shallow-level intrusions or volcanic eruptions. The rock is the hypabyssal or near-surface equivalent of diabase and is commonly found as dikes and sills, though it can also occur as layered intrusions. Dolerit forms when basaltic magma cools quickly at relatively shallow depths, producing small crystals typically less than a few millimeters in size. The principal minerals are plagioclase feldspar and pyroxene, with minor olivine. Quartz is uncommon. The color is usually dark grey to black, and the texture can range from aphanitic to porphyritic depending on cooling history.

Geology and distribution: Dolerit is widespread, occurring in many tectonic settings worldwide. It is especially common in regions with past volcanism and intrusive activity, such as continental rifts, volcanic arcs, and large igneous provinces. In outcrop, the rock may weather to a rusty brown rind due to iron oxidation.

Uses: Dolerit is used as crushed rock in road construction and as a base material for aggregates. When well-formed, it can serve as a dimension stone or decorative stone for architectural finishes.

Etymology and relation: The term dolerit is closely related to dolerite and diabase. In some languages the word dolerit specifically denotes the same rock type, while dolerite is the preferred term in others.

See also: Basalt, Diabase, Diorite, Igneous rock textures.