diabaasikivet

Diabaasikivet, also known as diabase or dolerite, are a type of mafic extrusive igneous rock. They are typically fine-grained to medium-grained and dark-colored, often appearing black or dark gray. Diabaasikivet are formed from the rapid cooling of basaltic magma that has erupted onto the Earth's surface or intruded into shallow crustal rocks. This rapid cooling prevents the formation of large crystals, resulting in their characteristic fine-grained texture.

The composition of diabaasikivi is similar to basalt, being rich in minerals such as plagioclase feldspar, pyroxene (like augite), and often olivine. They may also contain accessory minerals like magnetite and ilmenite. The texture is typically ophitic or subophitic, where laths of plagioclase feldspar are partially or completely enclosed by larger pyroxene crystals.

Diabaasikivet are commonly found in dikes, sills, and lava flows. They are significant in geological studies as they can provide insights into the volcanic history and tectonic settings of a region. Their durability and resistance to weathering make them suitable for use as building materials, particularly in construction and as decorative stone. In Finland, where the term "diabaasikivi" is used, these rocks are found in various geological formations.