♦Felsic: Light volcanic minerals e.g. feldspar. ♦:Porphyry Rocks containing large grains interbedded between small fine grains.
Granite is a felsic igneous rock created from solidified magma at depth. The main minerals in granite are quartz, mica and feldspar (plagioclase or potassium feldspar). Other minerals found in granite include hornblende and amphiboles. Granites are usually light to medium dark coloured (pinkish, greyish color) depending on the dominant mineral present. If granite consists of abundant quartz, it is usually light coloured. Granite is usually coarse grained but sometimes consist of interbedded coarse grains within fine granules (porphyritic texture). Granite is impervious, i.e it restricts water to pass through it, but if cracks and joints are available, water easily penetrates. The impervious nature, mineralogy, reflectivity of granite makes it resistant to weathering, unlike other rock types such as limestone that crumbles easily. Weathering processes such as exfoliation only operates within the outer layer (light minerals reflect insolation). Most physical weathering processes on granite produces blocks or cracks as the weathering products. As for chemical weathering, hydrolysis mainly attack the mineral feldspar into kaolin clay, but the other minerals are weathered slightly or remain intact. Comparing this to other less resistant rock types such as limestone that are weathered completely and washed away in solution, granite is resistant and often gets weathered by various processes to completely turn into clay.
Properties and Characteristics of Granite
formed from solidification of magma at depth
contains mainly quartz, mica and feldspar minerals
crystallined due to micas and quartz
light to medium coloured
medium coarse grains
durable and resistant to weathering
mineral feldspar crumbles rather easily under chemical reactions