Certain definitions of granite include the rock called quartz monzonite.
The tough, ash-colored rock called granite forms mammoth, dome-like mountains and, through human masonry, the equally imposing walls and floors of great buildings and monuments. Actually, the word "granite" can refer to a specific rock or to several related ones, including quartz monzonite. Does this Spark an idea?
Relative Hardness
The hardness of rocks, as measured by their resistance to abrasion, can be assessed on the Mohs scale. By this grade, which runs from one to 10, a mineral can scratch another of equal or lesser hardness. Rocks can be evaluated on the Mohs scale by considering their constituent minerals. Granite typically has a Mohs ranking between 5.5 and 7. The higher the proportion of quartz, which itself has a hardness of seven, the harder the given type of granite. Quartz monzonite, which tends to contain less quartz than granite, is of a hardness - 5.5 to 6 - similar to the low end of the granite Mohs scale.
Class of Rock
Both granite and quartz monzonite are igneous rocks, which, along with sedimentary and metamorphic types, constitute the major classes of rock. Igneous rocks are formed from solidified magma (molten rock sourced in the Earth's interior) or the searing liquids and gases associated with it (igneous comes from the Latin word for fire, "ignis"). Granite and quartz monzonite are further classified as plutonic or intrusive igneous rocks, which means they form when magma cools at depth, without reaching the planet's surface. Magma that does leak or explode aboveground (as lava) forms extrusive, or volcanic, igneous rock, examples of which include basalt and andesite.
Properties
Aside from its hardness, granite is characterized by a mineral profile heavy in quartz - often ranging between 20 and 60 percent - and feldspars. The rock is often phaneritic, which means it consists of an even grain, but much variety exists: Some granites show some large crystals embedded in fine-grained structure, which can be due to a marked shift in the rate of magma cooling in its formation. Depending on mineral type and proportion, granite usually ranges from pale to dark gray in hue. Quartz monzonite is typically medium- to coarse-grained, and often of a darker cast than granite. A monzonite rock is one with a quartz content of 10 percent of less; above that value, it is classified as quartz monzonite.
In the Environment
The ancient, fairly stable, highly durable cores of continental landmasses, called cratons -- and, where exposed at the Earth's surface, shields -- contain significant amounts of granite. The rock also composes the roots of many mountain ranges. Plutons of quartz monzonite and related rocks like diorite or granodiorite - all of them often classified casually as "granite" - can be exposed by the weathering and erosion of overlying materials to stand as mountain ranges. The Sierra Nevada in California is a well-known and striking example.
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