As one drives around the beautiful island of Mauritius, gentle slopes and deep valleys in brown and green can be observed. These features are carved on the volcanic rocks that created the island. Magma from deep inside the Earth’s crust has welled up and outpoured the thick mineral rich lava. Solidification over millions of years now results in an array of different types of rocks.
The study of rocks, called petrology, is fundamental to understanding a place’s history and evolution. For instance, the recent discovery of minerals in magmatic rocks has revealed the presence of a continental chunk under Mauritius. Fossils of plants and animals also get trapped inside of the rocks which again reveal a lot about past conditions.
Rocks are mainly minerals stuck together under certain conditions; hence their appearance, weight and uses vary from type to type.
There are basically 3 types of rocks:
Volcanic islands such as Hawaii, Mauritius, Java etc. are all made up of basically two types of rocks: basalt and granite. Basalt is composed mostly of calcic plagioclase feldspars and pyroxenes. It is normally dark in color and fine grained.
Two types of basalt can be found: tholeiitic basalt and alkalic basalt.
Tholeiitic basalt contains a high amount of silica and few alkalis like sodium and potassium. Alkali basalt, on the other hand, contains high amounts of alkalis and few silicas; the pyroxene is augite, made up of calcium and aluminium.
Both of them can contain olivine phenocrysts (crystals), feldspars or pyroxenes.
Granite is also formed as result of volcanic eruption, though it is formed right in the magmatic cauldron. It is light colored and usually contains quartz, amphiboles, feldspars, small amounts of mica and other minerals. These minerals give granitic rocks different tints.
Mauritius island was formed in two distinct phases: the old lava series and the recent lava series. For this reason, layers or rocks consisting of different minerals can be found. The old lava series regurgitated pristine magma which was a fusion of tholeiitic and alkalic basalt. Differentiation (changes in magmatic compositions due to temperature and pressures) formed picrite basalt at the base of the original volcanic shield, trachyte in the branched domes, ending in hawaiite and mugearite. The latter two rocks can still be seen on Mountain Blanche and Mountain Fayence.
The recent lava series, on the other hand, evolved from alkalic basalt magma; it didn’t go through much differentiation though.
There are both intrusive and extrusive types of rocks in Mauritius; most are fine grained while a few are coarse grained. Since the island emerged from the ocean floor through volcanic eruption, it is mostly made up of rocks in the basalt family.
The rocks of the island, from oldest to most recent, include:
Category: Terrestrial Environment Tags: ankaramite, erosion, extrusive rocks, hawaiite, igneous rocks, intrusive rocks, lava rocks, magmatic differentiation, marble. sandstone, mauritius, metamorphic rocks, mugearite, oceanite, phenocrysts, sedimentary rocks, slopes, trachyte, valleys, volcanic rocks, volcano, weathering
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