What does diabasic mean?
Diabasic is an adjective used almost exclusively in geology to describe material composed of, or characteristic of, diabase — a dark, fine- to medium-grained igneous rock of the same chemical composition as basalt but coarser in texture, because it cooled somewhat more slowly within the Earth's crust rather than erupting at the surface. The word most often appears in phrases such as 'diabasic texture', referring to the interlocking arrangement of plagioclase feldspar laths and pyroxene grains that gives these rocks their distinctive appearance under a microscope. Geologists may also speak of diabasic dikes, sills, or intrusions, since diabase typically forms sheet-like bodies that cut across older rock formations. Entirely formal and technical in register, the term carries no figurative use and would be unfamiliar to most general readers. Its rarity makes it useful chiefly in field reports, petrographic descriptions, and academic writing on volcanic and plutonic rocks.
adjectiveRelating to or composed of diabase, a dark, medium-grained igneous rock chemically equivalent to basalt but with a coarser texture due to slower cooling at shallow depths.
- Of or relating to diabase, a dark intrusive igneous rock intermediate in grain size between basalt and gabbro.
"The quarry yielded blocks of coarse diabasic rock used for road metal throughout the county."
"The diabasic dikes cutting through the sandstone were mapped by the survey team."
"Under the microscope the sample showed a classic diabasic texture, with plagioclase laths partly enclosed by pyroxene."
Despite sounding like a medical condition, 'diabasic' describes rock — and its Greek root means 'crossing over', because diabase intrusions literally cut across other rock layers as dikes and sills.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diabasic
Diabasic derives from diabase, the name of the rock it describes, combined with the adjectival suffix '-ic'. Diabase itself was borrowed in the early 19th century from French, which had taken it from Greek 'diabasis', meaning 'a crossing over', from 'diabainein', 'to pass through or cross'. The Greek root alludes to the way such rock forms intrusive sheets crossing other strata. The same Greek verb lies behind 'diabetes', literally 'a siphoning through', making the two words distant relatives despite their utterly different modern meanings.
Related word forms
How diabasic is actually used
Strictly technical vocabulary, confined to geology and petrography; rarely encountered outside scientific literature. In British usage the equivalent noun 'dolerite' is more common than 'diabase', so 'diabasic' appears correspondingly less often in British texts.
Easily confused with diabasic
Diabetic relates to diabetes mellitus, the metabolic disease, whereas diabasic is a geological term describing rock composed of diabase — the two share only a distant Greek root meaning 'to pass through'.