MARBLE : granite

Granite Information

Granite is a common, coarse-grained, light-colored, hard igneous rock consisting chiefly of quartz, orthoclase or microcline, and mica, used in monuments and for building.
Granite, coarse-grained igneous rock of even texture and light color, composed chiefly of quartz and feldspars. It usually contains small quantities of mica or hornblende, and minor accessory minerals may be present. Depending on the feldspar present, Granite may be pink, dark gray, or light gray. It is commonly believed to have solidified from molten rock (called magma) under pressure. However, some Granites show no contacts with surrounding wall rock, but instead gradually grade into metamorphic rock. Others show relic features found in sediments. This evidence suggests that some Granites are not igneous in origin, but metamorphic. Some Granites are the oldest known rocks on earth; others were formed during younger geologic periods. Crystallized at depth, Granite masses are exposed at the earth's surface by crustal movement or by the erosion of overlying rocks. Very coarse-grained Granite, called pegmatite, may contain minerals and gemstones of economic value. Such pegmatites are found in the Black Hills of South Dakota. Granite has been used since ancient times as a building material.Granite is a common and widely-occurring type of intrusive, felsic, igneous rock.
Granites are usually a white or buff color and are medium to coarse grained, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark grey or even black, depending on their chemistry and mineralogy.

Outcrops of Granite tend to form tors, rounded massifs, and terrains of rounded boulders cropping out of flat, sandy soils. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.

Granite is nearly always massive, hard and tough, and it is for this reason it has gained widespread use as a construction stone.

The average density of Granite is 2.75 g/cm3; with a range of 1.74 to 2.80.

The word Granite comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a crystalline rock.

Granite primarily consists of orthoclase and plagioclase feldspars, quartz, hornblende, biotite, muscovite and minor accessory minerals such as magnetite, garnet, zircon and apatite. Rarely, a pyroxene is present.

Granite is classified according to the QAPF diagram for coarse grained plutonic rocks (granitoids) and is named according to the percentage of Quartz, Alkali feldspar (orthoclase) and Plagioclase Feldspar on the A-Q-P half of the diagram. Highly peralkaline forms of Granite which are silica undersaturated may have a feldspathoid such as nepheline, and are classified on the A-F-P half of the diagram. See Figure 1, below.

True Granite according to modern petrology contains both plagioclase and orthoclase feldspars. When a granitoid is devoid of orthoclase the rock is referred to as alkali Granite or adamellite. When a granitoid contains <5% orthoclase it is known as a granodiorite, or tonalite when pyroxene is present.

A Granite containing both muscovite and biotite micas is called a binary or two-mica Granite. Two-mica Granites are typically high in potassium and low in plagioclase, and are usually S-type Granites or A-type Granites.

The volcanic equivalent of plutonic Granite is rhyolite.

The Red Pyramid of Ancient Egypt (c.26th century BC), named for the light crimson hue of its exposed Granite surfaces, is the third largest of Egyptian pyramids. Menkaure's Pyramid, likely dating to the same era, was constructed of limestone and Granite blocks. The Great Pyramid of Giza (c.2580 BC) contains a hugeGranite sarcophagus fashioned of "Red Aswan Granite." The mostly ruined Black Pyramid dating from the reign of Amenemhat III once had a polished Granitepyramidion or capstone, now on display in the main hall of the Egyptian Museum in Cairo (see Dahshur). Other uses in Ancient Egypt, [1] include columns, door lintels, sills, jambs, and wall and floor veneer.

How the Egyptians worked the solid Granite is still a matter of debate. Dr. Patrick Hunt [2] has postulated that the Egyptians used emery shown to have higher hardness on the Mohs scale.

Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. With increasingly acid rain in parts of the world, Granite has begun to supplant marble as a monument material, since it is much more durable. Polished Granite has been a popular choice for kitchen countertops due to its high durability and aesthetic qualities. The Black GalaxyGranites from Cheemakurthy area of Andhra Pradesh in India are world known for their elegance.

Engineers have traditionally used polished Granite surfaces to establish a plane of reference, since they are relatively impervious and inflexible.

Translations for: Granite

Nederlands (Dutch)
graniet(en), vastberadenheid

Français (French)
granit, de granit

Deutsch (German)
n. - Granit

Italiano (Italian)
granito, di granito

Português (Portuguese)
n. - granito (m), firmeza (f) (fig.)