Granite is an igneous rock that can vary greatly in color and composition. These factors depend on its mineral content, texture, and the circumstances of its formation. Granite is a strong and beautiful stone that has been used throughout history. It has been employed to construct buildings, monuments, roads, jewelry, and works of art. Many homes today use different types of granite for countertops or flooring. This is a stone that is durable, scratch-resistant, comes in a variety of colors, and can be polished to shine. Whether you’re an amateur rock enthusiast or investigating options for your kitchen remodel, read on to learn more about seven of the main varieties of granite, and pick your favorite.
How is Granite Made?
There are three main kinds of rock: igneous, sedimentary, and metamorphic. Granite is an intrusive igneous rock. This means that while it was still in a molten state, it cooled gradually within the crust of the earth. So, what does “gradual” mean? Geologists think some granite formed 10 miles below the surface of the planet. It then cooled over a period of one million years as it rose to the surface. This slow cooling process gave the mineral crystals in the stone time to grow very large. A person can see them with the naked eye. By contrast, ejected rock from volcanoes while still in a molten state cools quickly and forms small crystals. In fact, they are so small you can only see them through a microscope.
Granite usually contains 20-60% quartz, 10-65% feldspar, and 5-15% micas (biotite or muscovite). Types of granite stone with more mica may glitter with diamond-like sparkles. The color of the stone depends on its mineral content and the conditions of its formation. The most common colors for granite are pink, white, and different shades of grey and black. Because these are cheaper, they are the colors you are most likely to see in building projects and landscaping gravel. You might see the rarer and more expensive varieties in high-end interior design, jewelry, or fine arts.
These are some of the minerals that help create different beautiful colors of granite:
- Quartz – milky white
- Feldspar – off-white
- Potassium feldspar – salmon pink
- Biotite – black or dark brown
- Muscovite – metallic gold or yellow
- Amphibole – black or dark green
Granite comes in a very wide variety with numerous sub-categories. Here we will just describe 7 of the main categories based on color. It’s worth noting that these are just general descriptions of these types of granite and that there may be variations within each category. To truly identify a specific type of granite, consult a professional geologist or stone expert.
You can recognize this variety by its dark color, which comes in a variety of patterns, including solid black, speckled, or veined. Builders like to use it for high-end decorating applications, like countertop surfaces, flooring, and cladding. However, not everything marketed as black granite truly is granite. True granite must contain at least 20% quartz, so a completely black stone is more often gabbro, an igneous rock similar to basalt. True black granites should also include speckles of quartz, that glisten like stars in a night sky.
White granite is a light white or off-white color, often with gray or black flecks throughout. Like black granite, it’s a popular choice for beautiful and durable countertops, tiles, and flooring. The main sources of its white color are the minerals quartz and feldspar. The black flecks are often small grains of amphibole. A completely white countertop or tile advertised as granite is likely a man-made rock. These rocks are created to simulate granite or quartz.
Speckled Black and White Granite
Speckled black and white granite looks exactly like what it sounds like: a stone that is white with large flecks of black and grey in it. Quartz, amphibole, and feldspar are the culprits that create this combination. Looking at it, it looks a bit like abstract art. Our brains enjoy sorting complex random information and looking for patterns, so maybe at a subconscious level, this type of stone creates an intriguing mind puzzle for us. It is less expensive than some of the other varieties, so you are likely to see it more often than them. If you look around your neighborhood, workplace, or even your own house, you might find some examples in building stones, countertops, flooring, landscaping gravel, or monuments. Additionally, it is often in gravestones.
Pink granite is a truly extraordinary type of granite that comes in a wide range of different shades of pink or rose. The pink color comes from potassium feldspar in the stone. Small specks of semi-transparent quartz make this type of granite glitter. You’ll also notice dark spots, which are brown or black amphibole, and white flecks of opaque feldspar. The color patterns make this type of granite a popular choice for countertops, flooring, and building exteriors. Looking at it, it’s hard to imagine it occurs naturally without any artificial manipulation to create such a beautiful combination.
Green granite ranges in shade from pale to dark. It is one of the rarest types of granite stone. It sometimes occurs when it includes amazonite, a type of green feldspar. If it is important to you to get actual green granite for your project, you could look for varieties called Verde Ubatuba, Verde Labrador, Amazon Green, or others. Be aware that some stones marketed as granite are actually either soapstone or marble colored green by serpentine.
Red granite is a variety that contains a high quantity of pink potassium feldspar of a shade that is more red than pink. A red coloration can also result from contamination of the feldspar with hematite grains or iron oxide (rust).
This one is tricky. Advertisers often say blue granite is one of the rarest and most beautiful varieties. However, most of what is commercially available is not granite at all, but larvikite, an igneous variety of monzonite (with less than 5% quartz), or anorthosite, a rock that contains blue labradorite and no quartz. Although they do not meet the technical definition of granite, they come in similar textures, durability, and beauty.
Where and How Granite is Mined
The world’s largest exporters of various types of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain, and the United States. The U.S. states that produce the most granite are Texas, Massachusetts, Indiana, Wisconsin, and Georgia – but in fact, most U.S. states produce at least some granite.
Granite quarries are usually in areas where erosion has exposed an underlying granite formation. It is usually extracted as crushed stone or dimension stone in open pit mines. The mining process begins by removing the overburden, or the soil and rock above the granite deposit. They use large earth-moving equipment, such as bulldozers and excavators. Once the overburden is removed, the granite can be extracted using drilling and blasting techniques, or by using specialized cutting equipment to carve out large blocks of granite.
After mining raw granite, technicians use heavy machinery to transport and unload the stone at a processing facility. Using diamond-tipped saws, experts cut these hard stones into smaller and more manageable pieces. To get a polished surface, specialists use diamond-coated sanders and polishers of increasingly fine grades to get a high sheen. After cutting and polishing, they inspect the granite for flaws, then they ship it out to distributors for the commercial and consumer markets.
Environmental Impact of Granite Processing
Granite processing, like any industrial harvesting of raw materials, can impact the environment negatively. It alters the landscape, disturbing natural biomes. Run-off and erosion from mining sites can contaminate rivers for miles downstream. Dust particles create air pollution that can affect both workers and people living in any area downwind. The heavy machinery required to do the work and deliver the final product is resource intensive, requiring a lot of diesel fuel and electricity that leave a large carbon footprint. And don’t forget that, while plentiful, granite itself is a non-renewable resource.
When you choose granite for your project, you have not only a wide choice of colors, but of production sources as well. If the environmental impact of granite mining is something you are concerned about, ask questions at your retailer about their sources and do a little investigation to learn about the mining and production company and its processes. With some research, you’ll be able to find an ethically-sourced material that is beautiful and durable enough to enjoy for a lifetime.
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