Obsidian ridge by Mt. Krafla. Jörundur, a nearby mountain, can be seen in the distance. Photograph: Kristján Jónasson.
Rocks are typically composed of an assortment of minerals or clasts. There are three main types of rock: igneous, sedimentary and metamorphic rock. Iceland is composed mainly of igneous rock – sedimentary rock accounts for only 8-10% of Iceland's volume, and there is no true metamorphic rock on the island. Igneous rock is classified on the basis of its chemical and mineral composition. A distinction is also made between volcanic rock (formed when magma is erupted to the surface and solidifies there) and plutonic rock (formed when magma solidifies below the surface). As Iceland is a young country in geological terms and little eroded, volcanic rock is dominant.
A total of 25 types of igneous rock have been found in Iceland, the most common of which are tholeiite, olivine tholeiite, gabbro and rhyolite. The main rock-forming minerals in tholeiite and olivine tholeiite are plagioclase, augite, olivine, magnetite and apatite. Icelandic igneous rock forms three rock series: the tholeiitic series, transitional series and alkalic series.
The systematic collection and analysis of Icelandic rock species at the IINH began in 1970. Research at the IINH on Icelandic rock and its origin and distribution has focused on basic and silicic rock and the formation of palagonite tuff.