kivilajit

Kivilajit are naturally occurring, coherent solids composed primarily of minerals. In geology, the term refers to broad categories of rocks distinguished by their origin and formation processes. The three principal groups are igneous, sedimentary, and metamorphic rocks.

Igneous rocks form when molten material crystallizes. If cooling happens underground, the rocks are intrusive (plutonic) and tend to have visible crystals; if cooling occurs at the surface, they are extrusive (volcanic) and typically fine-grained or glassy. Common examples include granite and diorite (felsic to intermediate plutonic), and basalt, rhyolite, obsidian (mafic to felsic volcanic).

Sedimentary rocks originate from the accumulation and lithification of sediment or from precipitation of minerals from water. They are often subdivided into clastic rocks (such as sandstone and shale), formed from broken fragments, and chemical/biochemical rocks (such as limestone and coal), formed by precipitation or organic processes. Sedimentary rocks commonly display features like bedding, fossils, and ripple marks.

Metamorphic rocks arise from existing rocks transformed by heat, pressure, or chemically active fluids. They are broadly categorized as foliated (slate, schist, gneiss) due to aligned minerals, and non-foliated (marble, quartzite) where new minerals form without alignment. Metamorphism can alter texture, mineralogy, and density without melting.

The rock cycle describes how kivilajit can transform from one type to another through weathering, burial, tectonics, and metamorphism. In many regions, including the Fennoscandian Shield, kivilajit reflect long geological histories, with granites, gneisses, and other ancient rocks constituting the bedrock.