Morphological characteristics of granite

Although granite is a good building material, granite in some areas emits radon, a naturally occurring radioactive gas. Radon can cause lung cancer, and in Hong Kong, 13% of lung cancer deaths are attributed to excessive radon levels.

Granite, a coarse-grained or medium-grained intrusive rock rich in quartz and feldspar, is the most common plutonic rock in the Earth's crust, formed by the cooling of magma deep within the crust. Granite quarrying was once an important industry due to its use as paving stones and building material.

Granite can occur as dikes or sills, but more typically as irregular bodies of greatly varying size. The main component is feldspar, with both plagioclase and alkali feldspar generally abundant; their relative abundance forms the basis for granite classification. In most granites, the ratio of these two types of feldspar is less than 1/2. This type includes most granites in the eastern, central, and southwestern United States, southwestern England, the Baltic Shield region, western and central France, Spain, and many other areas. Granites where plagioclase greatly exceeds alkali feldspar are common in some areas of the western United States. Granites with a much higher content of alkali feldspar than plagioclase occur in New England, many locations in Britain and the Oslo region of Norway, but these are generally smaller bodies, although they are extensively developed in northern Nigeria. Rocks with less than 20% quartz are not called granite, and the maximum content of dark minerals (ferromagnesian minerals) is approximately 20% (by volume). Less common major minerals in granite include muscovite, biotite, amphibole, pyroxene, or rarely fayalite. Biotite can occur in any type of granite and is usually present, although sometimes in small amounts. Sodium-bearing amphiboles and pyroxenes (riebeckite, arfvedsonite, aegirine) are characteristic of alkaline granites. If neither type of feldspar greatly exceeds the other, then amphibole and pyroxene are unlikely to be major minerals; the dark minerals are usually biotite or muscovite, or both.