Thin layers of iron formation occur within other rocks in northern Minnesota. The term is a contraction of "iron-bearing formation" which is a rock having as much as 30 percent iron in places. Iron formation formed when iron-rich particles precipitated and settled to the sea floor during quiet periods in volcanic activity.
Basalt is a very common volcanic rock with low silica content. Rhyolite is a volcanic rock with high silica content. Rhyolite has silica content similar to that of granite while basalt is compositionally equal to gabbro. Intermediate volcanic rocks include andesite dacite trachyte and latite. Pyroclastic rocks are the product of explosive ...
Felsic composition is higher in silica SiO 2 and low in iron Fe and magnesium Mg . Mafic composition is higher in iron and magnesium and lower in silica. Intermediate compositions contain silica iron and magnesium in amounts that are intermediate to felsic and mafic compositions. Composition and Color
Basalt magma is formed at high temperatures around 1200ºC . When it comes out of the volcano it is hot and liquid. It contains very little silica less than 50% and a lot of magnesium and iron which makes the rock look dark.
Gabbro is a dark-colored igneous rock that is considered to be the plutonic equivalent of basalt. Unlike granite gabbro is low in silica and has no quartz. Also gabbro has no alkali feldspar only plagioclase feldspar with a high calcium content.
Mafic rocks have a relatively low silica content and are composed mostly of pyroxenes olivines and calcic plagioclase. These rocks basalt gabbro are usually dark coloured and have a higher density than felsic rocks. Ultramafic rock is very low in silica with more than 90% of mafic minerals komatiite dunite .
Basaltic Magmas have comparatively low silica contents about 50% and have temperatures between 900 and 1200 degrees Celsius. They are rich in iron and magnesium and form through partial melting of the upper mantle from peridotite in areas of mantle upwelling and high heatflow mid-oceanic ridges; continental rifts .
Alkali basalt is relatively poor in silica and rich in sodium. It is silica-undersaturated and may contain feldspathoids alkali feldspar and phlogopite. Alkaline Basalt. Boninite is a high-magnesium form of basalt that is erupted generally in back-arc basins distinguished by its low titanium content and trace-element composition. Petrology ...