Diabase

Diabase (/ˈdaɪ.əˌbeɪs/), also called dolerite (/ˈdɒl.əˌraɪt/) or microgabbro,[1] 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 to aphanitic chilled margins which may contain tachylite (dark mafic glass).

[3] Accessory and alteration minerals include hornblende, biotite, apatite, pyrrhotite, chalcopyrite, serpentine, chlorite, and calcite.

[4] The feldspar is high in anorthite (as opposed to albite), the calcium endmember of the plagioclase anorthite-albite solid solution series, most commonly labradorite.

[6] In the Death Valley region of California, Precambrian diabase intrusions metamorphosed pre-existing dolomite into economically important talc deposits.

One geotourist attraction is the Steinerne Rose near Saalburg, a natural monument, whose present shape is due to the typical weathering of lava pillows.

[15] The vast areas of mafic volcanism/plutonism associated with the Jurassic breakup of the Gondwana supercontinent in the Southern Hemisphere include many large diabase/dolerite sills and dike swarms.

Here, the volume of magma which intruded into a thin veneer of Permian and Triassic rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres.