Granite 101

For thousands of years, granite has been a popular building material, not just for countertops and tiling, but for everything from buildings, monuments, and gravestones to bridges and roadways. It was used, along with limestone, to build Egypt’s pyramids, and much of ancient Rome’s columns and monumental buildings were carved from granite.

So what makes it such a popular material, what is granite exactly, and what are the different types and applications? Consider this your primer.

What is granite?

One of the world’s most prevalent natural stones, granite is believed to be solidified magma, slowly crystallized over time under pressure from the earth’s crust. This classifies granite as an igneous rock, a type of rock formed from the solidification of molten rock (magma). The slow cooling process beneath the Earth’s surface enables granite’s large crystals to form. Igneous rocks cooled above the surface cool faster, forming smaller crystals or no crystals at all. Obsidian is a perfect example of this kind of igneous rock; its smooth, glass-like surface is crystal-less.

Granite is coarse-grained (its mineral contents are easily seen by the naked eye) and light-colored, composed mostly of the minerals feldspars and quartz, with other trace minerals, in varying quantities,like mica and amphibole. This unique composition makes granite easily recognizable and identifiable; it also provides its wide range of colors. Feldspar gives granite a red or pink color, mica contributes dark brown or black, quartz is generally clear white, pink, or black, and amphibole is black.  

Where does granite come from?

In the United States, granite quarried for building materials like countertops comes mostly from five states: South Dakota, Idaho, Massachusetts, Georgia, and New Hampshire.

Granite is not only the earth’s most common igneous rock, it’s also the most well-known, recognizable from monuments and buildings to some of our most famous natural treasures. Yosemite Valley in California is a showcase of steep granite cliffs, as are Pike’s Peak, Colorado, the White Mountains in New Hampshire, and Stone Mountain, Georgia. And Mount Rushmore’s famous busts are carved from a massive granite cliff.

Wait — I thought granite was formed under the earth’s surface?

It is — the large size of the crystals in granite rock indicate that granite is an igneous rock, formed by slow cooling of magma underneath the earth’s surface. These large deposits of granite become exposed above the surface, forming cliffs, mountains, and other natural structures, by both the movement of the earth’s tectonic plates or the erosion of overlying rocks.

Why is it such a popular countertop material?

It’s popular for a variety of both interior and exterior building projects — it is strong enough to support a significant amount of weight, durable and scratch-resistant, weather-resistant, and can be polished to a high shine. It also goes through a process called case-hardening, which causes granite to become even harder with age.

In exterior projects, such as building exteriors, bridges, pavement, and monuments or statues, granite is used both rough-cut and polished. Polished granite slabs and tiling are more popular than rough-cut for indoor projects, including countertops, backsplashes, flooring, stair treads, and more.

Granite has also long been a popular material for gravestones and memorials, due to its stateliness and durability. It wasn’t until the 18th century, and the invention of steam-powered cutting tools, that granite headstones were able to easily be marked and carved — prior to this invention, they were hand-carved, resulting in poor readability.

As a countertop material especially, granite is popular because it meets a sweet spot of durability — it resists most abrasions, water, mold, and heat and has a low chemical reactivity — quality, and aesthetics that make its relatively higher price fair. It also comes in such a wide variety of colors and crystal content that makes it easy to find a color and grain you love.

What are the different types of granite?

When it is quarried, granite is collected both as crushed rock and large stone slabs — called dimension stone. As crushed rock, it is widely used in both road construction and railroad beds. While crushed limestone is the most popular crushed rock in the U.S. (70% of crushed rock is limestone), granite is the second most used crushed rock, representing 16% of crushed rock consumption, or 265,000 tons per year.

Approximately 400,000 tons of slab granite (27% of all dimension stone) are produced each year in the U.S., second, again, only to limestone in terms of volume and popularity. As we’ve mentioned, granite can be either rough-cut or polished, and used as slab countertops, building stone blocks, tiles, pavers, and crushed stone.

When it comes to different granite colors, they mostly range from pink and white to grey and black.

White Granite

When granite is mostly composed of quartz (a milky white color) and feldspar (a more opaque white), the result is white granite. White granite, however, is never 100% white due the presence of other minerals, so it will typically take on a “salt-and-pepper” look, with the white “salt” being the most prevalent. This creates a stone that is primarily white with small black “pepper” specks, generally the mineral amphibole.

Some of the more popular named types of white granite include:

  • Kashmir White, a metamorphic white rock with deep red crystals, made mostly of white feldspar and quartz
  • Giallo Ornamental, primarily white from feldspar and quartz
  • Bianco Antico, mostly white quartz with pink feldspar specks

Black Granite

Similarly, black granite is never 100% black — it will generally have specks of other, lighter colored minerals as well. It is also not technically true granite, but more likely another igneous rock called gabbro. What makes it not a true granite? Black granite doesn’t contain 20% or more of quartz. Because of its similarity to granite both in makeup and aesthetics, however, grabbo is commonly, commercially referred to as black granite to simplify material selection.

Some of the more popular named types of black granite include:

  • Absolute Black, a type of grabbo
  • Black Galaxy, a type of grabbo that is black with golden specks
  • Uba Tuba, mined in Brazil, Uba Tuba gets its color from mica

Black and White Granite

Black and white granite is a true granite, composed of more equal parts quartz, amphibole, and feldspar than white granite. This is one of the most common types/colors of granite and one of the most popular materials for countertops.

One of the most popular named types of black and white granite is Black Pearl, a grabbo with both ampibole and pyroxene.

Brown Granite

Brown granite is a common choice equally for its neutral tones and rich variety of colors. Brown granite ranges from light and golden tans to deep chocolate and even burgundy browns, and can feature both large and small quartz crystals.

Some of the more popular named types of brown granite include:

  • Venetian Gold, tan and white quartz and feldspar with black, grey, and red specks from amphibole, mica, and garnet
  • Tan Brown, large amounts of feldspar with small amounts of potassium for a pinkish tint, along with brown and black specks, likely from amphibole
  • Baltic Brown, similar to tan brown, with larger grains of feldspar

Pink Granite

An abundance of the mineral potassium feldspar, combined with small amounts of quartz, amphibole, and even white feldspar, gives pink granite its salmon color.

Some of the more popular named types of pink granite include:

  • Copper Rose, featuring waves of pink feldspar through milky quartz and dark specks
  • Milford Pink, a light pinkish gray with dark greenish-gray spots from soda lime feldspar

Red Granite

Red granite gets its color simply from a variation of potassium feldspar which causes its pigment to be more red than pink. These granites are among the most rare and sought-after types of granite.

Some of the more popular named types of red granite include:

  • Santa, or St. Cecilia, with many deep reds along with tans from feldspar, quartz, and biotite
  • Imperial Red, a deep burgundy
  • Havana Red, a reddish brown quarried in Saudi Arabia and China

 

By | 2017-10-07T02:30:58+00:00 October 7th, 2017|Uncategorized|0 Comments

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