Granite, quartz and feldspar are typical examples.Add rocks are hard, compact, massive and resistant to weathering.High mountains are formed of this type of rock.Due to the excess of silicon, acidic magma cools fast, and it does not flow and spread far away.These rocks constitute the sial portion of the crust.Hence, they are less dense and are lighter in colour than basic rocks. These rocks have a lesser content of heavier minerals like iron and magnesium.The rest is divided among aluminium, alkalis, magnesium, iron oxide, lime etc.Acidic rocks are characterised by high content of silica (quartz and feldspar) - up to 80 per cent.
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