<P> By definition , basalt is an aphanitic ( fine - grained ) igneous rock with generally 45 - 53 % silica ( SiO ) and less than 10 % feldspathoid by volume , and where at least 65 % of the rock is feldspar in the form of plagioclase . This is as per definition of the International Union of Geological Sciences ( IUGS ) classification scheme . It is the most common volcanic rock type on Earth , being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands , including Iceland , the Faroe Islands , Réunion and the islands of Hawaiʻi . Basalt commonly features a very fine - grained or glassy matrix interspersed with visible mineral grains . The average density is 3.0 g / cm . </P>
<P> By definition , basalt is an aphanitic ( fine - grained ) igneous rock with generally 45 - 53 % silica ( SiO ) and less than 10 % feldspathoid by volume , and where at least 65 % of the rock is feldspar in the form of plagioclase . This is as per definition of the International Union of Geological Sciences ( IUGS ) classification scheme . It is the most common volcanic rock type on Earth , being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands , including Iceland , the Faroe Islands , Réunion and the islands of Hawaiʻi . Basalt commonly features a very fine - grained or glassy matrix interspersed with visible mineral grains . The average density is 3.0 g / cm . </P>
where do most rocks have a basaltic composition
where do most rocks have a basaltic composition
being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands , including Iceland , the Faroe Islands , Réunion and the islands of Hawaiʻi
being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands , including Iceland , the Faroe Islands , Réunion and the islands of Hawaiʻi