What is Granite?

Granite is—quite literally—as old as the earth. It is formed from liquid magma, the molten rock still found at the core of the planet, cooled slowly to form a substance approaching the hardness and durability of diamond. Granite is an igneous rock, the name reflecting its fiery beginnings. The chemical composition of granite is similar to that of lava. However, granite owes its hardness and density to the fact that it has been solidified deep within the earth, under extreme pressure. Over the eons, seismic activity has changed the crust of the planet, forcing veins of granite to the surface. Glaciers scraped off layers of dirt, sand and rock to expose granite formations. Typically revealed by outcrops, the deposits have been discovered on all the continents.

It is accurate to speak of "granites," because many varieties of the stone exist. While they differ in color, texture and crystalline structure, the granites have three essential minerals in common: Feldspar, Quartz, and Mica.

These minerals occur in different proportions, giving each granite its own color, texture and structural characteristics. In addition, hornblende, magnetite, hematite, pyrite, zircon, garnet, corundum and other minerals may be present in smaller amounts, adding to the unique coloration and texture of each granite deposit. In supplying granite for a large building or complex of buildings, it is essential that the stone be consistent in color and texture. To assure this, each granite color must be quarried from the same deposit. With natural material like granite, a certain amount of "movement" or grain in the stone must be expected. Many people find this flow and blending of colors to be the most compelling reason for using granite.

Comparing Granite to Other Building Materials

There are several different types of building stone on the current market. At The Granite Gallery, they include common stone such as granite, marble, limestone, travertine, as well as the man-made CaesarStone™. Each stone has unique physical characteristics, which affect its applicability to various building designs. This section describes the characteristics and physical properties of the major building stones.

Granite

Granite is an igneous rock created deep within the earth from magma, cooled slowly under great pressure. It is the hardest building stone with very dense grain, making it virtually impervious to stain. It takes a highly polished finish, which will endure even in inclement environments. It also can be finished in a variety of other ways. There is a broad spectrum of granite colors ranging from nearly pure white to nearly pure black. During its formation, granite may also have been infused with other minerals providing patterned "movement" as well as color.

Most common uses: Interior and exterior wall cladding, interior and exterior paving, residential & commercial counter tops, monuments, curbing, statuary, balance tables, novelty items, etc.

Marble

Marble is a metamorphic rock, composed of metamorphosized limestone. In its purest form, marble is crystalline white calcite. Most marbles, however, are infused with impurities such as dolomite, silica or clay, providing variations in color and significant movement. The base colors of marble range from white to black with a broad range of hues. Marble is significantly softer than granite and therefore subject to greater wear and weathering.

Most common uses: Interior and exterior wall cladding, Interior and exterior paving, Fireplace facing and hearth, Lavatory tops, Residential & Commercial counter tops, Table Tops, Statuary, Novelty items, Many non architectural uses, such as tooth paste, paint whiting, agricultural lime, etc.

Limestone

Limestone is a sedimentary rock composed of calcites and dolomites. Organic limestones were formed from the deposits of marine shellfish and fossils. Limestone is noncrystalline and possesses very uniform composition, texture and structure. It is soft and therefore easy to quarry and shape. Limestone ranges in color from white to gray and does not take a polish.

Most common uses: Interior and exterior wall cladding, interior and exterior paving, limited counter top use

Engineered Stone

Most common uses: Kitchen countertops & backsplash, bath vanity tops, tabletops, fireplace surround

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Physical Properties of Building Stone

All stones are natural materials subject to variation in properties according to specific mineral composition, size and thickness of the tested piece.

Coefficient of Expansion

Stone expands and contracts minimally with temperature change. Normally the amount of change is too insignificant to cause a problem. However, some of the purest marbles retain a small incremental change after each heating cycle. This is called hysteresis. In thin veneers, it can put strain on the backing material and cause bowing and even rupture. This also increases the porosity of the stone, making it more susceptible to attack from atmospheric acids and cyclic freezing. In granite and limestone, the amount of change is in millionths of an inch—usually not enough to cause problems. In some marbles and sandstones, the coefficient is in hundred-thousandths of an inch, which could cause problems. In most construction systems, the normal fasteners and joint materials accommodate minor expansion and contraction of the stone.

Weathering

Stone generally weathers better than other building materials; however, not all stone endures equally well. Some are subject to greater damage from freezing and thawing and attack from sulfurous and sulfuric acid, carbonic acid and ammonium salts. Granite is nearly impervious to weathering from temperature changes and from airborne chemicals. In fact, granite is so resistant to chemical erosion that granite tanks are often used to store highly caustic materials.

Freeze/thaw weathering rarely occurs in polished granite surfaces. Weather damage to granite with any finish is extremely uncommon because of its inherently low absorption rate.

Permeability

Granite is significantly less porous than other building stones, yet it is capable of absorbing moisture. Fabrication is a "wet" process: the cutting of granite is accomplished with a slurry of water and abrasive material. Sometimes granite is shipped before it is completely dried, and the moisture absorbed during fabrication gives the granite a different color than in its dry state. Such stones will dry in relatively short order and return to their true color. Once dry, the atmospheric moisture precipitation and humidity will not normally penetrate the stone.

Variegation

Granite is very consistent in color and texture when compared to marble, however, granite also exhibits movement and color variation.