Commercial Granites
Granite Description
Granite is a light-colored plutonic rock found throughout the continental crust, most commonly in mountainous areas. It consists of coarse grains of quartz (10-50%), potassium feldspar, and sodium feldspar. These minerals make up more than 80% of the rock. Other common minerals include mica (muscovite and biotite) and hornblende (see amphibole). The chemical composition of granite is typically 70-77% silica, 11-13% alumina, 3-5% potassium oxide, 3-5% soda, 1% lime, 2-3% total iron, ...True Granites vs. Commercial Granites
Granites in the commercial sense are hard natural stones which are polishable and need to be worked on by harder tools than for marble for cutting, shaping and polishing. They are usually suitable for interior and exterior use. Thus have different geological origins and minerals. Petrographically, they are either magmatic or metamorphic rocks. ...True granite and true marble
Comparison of true granite and true marble. Schematic images are magnified.In commercial granites, the larger the grain size, the lower is the strength, and the greater is the brittleness, because mineral cleavage can occur more easily in larger grains. A homogenous structure or a mildly-oriented one is a feature of magmatic rocks & so they have a similar appearance (structure) even over a large area of a slab. Metamorphic rocks are characterised by structures with bands, schlierens, & waves & so every part of a slab usually has a different appearance. ...
Metamorphic Rocks
METAMORPHIC ROCKS were formed by the recrystalization of sedimentary or magmatic rocks under the earth's surface during raised pressure and temperature conditions, from low to high grade metamorphism.(Commercial slates are metamorphic rocks exposed to low metamorphism. High metamorphic rocks such as gneisses belong to commercial granites.)
Water Absorption
WATER ABSORPTION BY WEIGHTThe percentage of water absorption into stone by weight is determined by the ratio of the weight of absorbed water and the stone weight. Values in brackets are less reliable because of small amount of data available or estimation done according to similar stones. Absorbency has a correlation with staining & is this a factor for selection for countertop & other application ...