Wednesday, 18 March 2015

Gabbro

Gabbro

Gabbro is an intrusive igneous rock, coarse grained, dark coloured and consists mainly of calcium rich plagioclase feldspar and clinopyroxene. Minor amount of olivine, biotite, magnetite, apatite, ilmenite and orthopyroxene can also be the constituent mineral. Gabbro is very low on silica content thus have little to no quartz content.

Colour

The colour of gabbro is black or dark green which is by the constituent mineral content. 

Equivalent rock

Gabbro extrusive equivalent rock is basalt which is an extrusive igneous rock the only difference is the grain size as basalt is extrusive which cools rapidly giving fine grained texture.

Ocean crust rocks

The oceanic crust deep inside earth crust is made up of gabbro due to it slow cooling rate, the grains are coarser. At the surface of the ocean crust, basalt is abundant which is an extrusive rock. The temperature at the surface is cooler compare to interior portion so basaltic grains will be finer.

Gabbro in continental crust

On the continent, gabbro can be found in thick lava flows of basaltic in nature where cooling rate is slower allowing crystals to grow larger. These can also be found where magma chamber feed the continental crust and when it dies the cooling rate will be enough to grow large crystal which will in turn make gabbro deposits.

Gabbro serving as ore

Gabbro have sometimes associated minerals which can be mined. Gabbro contains mineral ilmenite which can be mined for its titanium content and other can be mined for nickel, chromium or platinum.

Uses of gabbro

The most common use of gabbro is as a crushed stone or aggregate in construction projects as road construction. It can also be used as a brittle polish gabbro for cemetery markers, floor tiles, facing stone etc. It can also be used as a dimension stone.

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