diabaasi

Diabaasi, known in English as diabase, is a dense, mafic igneous rock that lies between basalt and gabbro in composition. It is typically dark-colored, with a fine- to medium-grained texture, and commonly occurs as intrusive bodies such as dikes and sills, or as a coarse-grained equivalent in some settings. The rock is also referred to as basaltic dolerite in many classifications. In the field it may appear as porphyritic or non-porphyritic, and its appearance ranges from dark gray to nearly black.

The mineralogy of diabase is dominated by plagioclase feldspar and pyroxene, with olivine present in some varieties. Accessory minerals can include magnetite, ilmenite, and minor amphibole. The chemical composition is typically in the basaltic range, roughly 45–52% silicon dioxide, with relatively low amounts of volatiles compared with more felsic rocks. The texture reflects crystallization at shallow crustal depths, producing fine to medium crystals that crystallized from a cooling magma.

Geologic setting and formation: diabase forms when magma intrudes the crust and crystallizes at shallow depths, often forming dike swarms or sill complexes. It is associated with tectonic regimes that produce basaltic magmatism, including continental rift zones and some oceanic crustal features. Uses of diabase include crushed stone for construction, road base, and sometimes dimension stone for facing and decorative work, reflecting its hardness and durability.

Diabase is widespread and studied for insights into crustal magmatism and intrusive rock processes. Its practical value lies in construction materials and as a source of aggregate in many regions.