Granite is one of the most commonly found rocks on the surface of the earth. It has a lot of excellent properties that make it an excellent tool for construction aggregation as well as learning purposes. The question is, Granite Intrusive or extrusive is, therefore, a common among many people. The coarse-grained rock is made up of different elements, including quartz and feldspar, and its formation makes it an Intrusive rock. The terms magma and lava have been used interchangeably for a long time and rightfully so. The only difference between these terms is their exposure. When still below the ground, it is known as magma, but when it bursts through, it becomes lava. These terms are important because they determine the formation of rocks. The types of rocks formed by magma underground are different from the types of rocks formed by lava. This leads to the terms of Intrusive and extrusive rocks.
Intrusive and Extrusive rocks
Being underground means that the magma cools at a very slow pace. This reduced cooling process leads to the formation of minerals that join together to create large crystals that are visible to the naked eye. This leads to the formation of different types of rocks, Granite being one of them. This formation process is the reason why Intrusive rocks have different colors. They are a result of different minerals joining together to create one big rock. Unlike Intrusive rocks, Extrusive rocks are formed by lava. When magma finds its way onto the earth's surface, it cools and hardens faster, leading to the formation of invisible crystals. The fast cooling process doesn't allow the crystals to harden and become big enough to be seen without a magnifying glass. As a result, you won't be able to see them as individual crystals but will see a whole rock. This is why Extrusive rocks don't have multiple colors.
In some cases, they even form glass instead of grains. The glasses are classified into three categories depending on how they are formed. For instance, if an extrusive rock comes out as glass with large bubbles, it's called scoria. However, if the bubbles are tiny, it's called pumice. If the bubbles are minimal, the rock is called obsidian.
Is Granite an Intrusive or Extrusive Rock
Granite has a lot of different colors ranging from white to pink. This doesn't just make them visually pleasing but also makes them one of the best choices when it comes to different construction types. These colors are a result of the rock being intrusive instead of extrusive. Something that has also contributed to the durable and strong nature of the rock. Apart from the colors, another reason why Granite isn't extrusive is the significant visible minerals. As stated above, extrusive rocks don't have minerals large enough to be obvious. It doesn't mean that the minerals do exist; they are just not large enough to be seen. Granite is formed naturally, but sometimes it can be manufactured. It's therefore advisable to be keen when shopping for one because the manufactured ones are always as strong and long-lasting as the natural ones.
Granite rocks are usually found near the surface that further down and are usually a product of continental crust. These rocks aren't very dense and, as such, will often try to move towards the surface as they cool. This also makes it easier for the Granite to expand when the material covering it on the surface is swept off by natural occurrences like erosion. This is possible because of the hydrolysis process that forms the rock and is another reason why granite rocks are not extrusive.
When molten rock cools underground, the cooling process of each mineral differs. This difference allows the minerals to form different colors. As they continue to cool at different rates, they join together to form Granite. This means that the size of each crystal will depend on how long it cooled off. It also determines the different colors of Granite and subsequently, the type. The major types of minerals found in Granite include feldspar, which is off white, quartz, which is milky white, biotite, which is dark brown or black and muscovite, which is yellow or metallic brown. There is also the amphibole, which is dark green but sometimes black as well as potassium feldspar, which is salmon pink. Based on each of these mineral content, you'll end up with different types of Granite, namely:
This type of granite mostly consists of quartz and feldspar minerals. Even so, it is usually not just white but is laced with some black particles. This interesting blend arises from the availability of amphibole mineral but is very small quantities. Most of the time, this results from a lack of enough amphibole in the molten rock. Also, the inability of amphiboles to cool as fast as the quartz and feldspar. Natural White Granite will always form this composition. Those that are purely white are most likely man-made and not naturally formed.
To understand the different types of granites, you have to follow the percentage of mineral composition. Natural Granite must always have at least 20 percent quartz. The other minerals may vary with feldspar being at least 10 percent and biotite and muscovite being at least 5 percent. This means that black Granite doesn't exist even though you'll always find some people using that name to drive sales. Most of the time, what is sold as black Granite is gabbro, another intrusive rock that doesn't have the same composition or qualities of Granite. Even though they are both intrusive, gabbro is made up of a very little amount of amphibole and more olivine, pyroxene, and plagioclase.
As mentioned above, potassium feldspar mineral is what has the salmon pink color. As such, it is responsible for the pink color in Granite. This means that pink Granite has more of potassium feldspar but there will always be white feldspar and quartz. You'll also notice a little bit of black amphibole. This mixture results in an exciting color combination that makes the Granite perfect for different uses. You should stay away from any Granite that is purely pink because chances are, it isn't authentic
Black and White Granite
While there's no such thing as black Granite, black and white Granite does exist. A great example of black and white granite is Valle Nevado Granite. This is made up of white quartz and black amphibole. You'll also find a small composition of white feldspar leading to a pretty mixture of black and white/opaque and sometimes dark green because of the amphibole. This type of Granite is very common and is mostly used in the real estate sector to make countertops.
Although it isn't widespread, the red Granite looks just as pretty as the others. It is mostly made up of potassium feldspar with different variations. When the molten rock mainly consists of this type of mineral, the colling process may still not be uniform. This leads to a difference of colors even though it's the same mineral. As a result, you get darker shades of pink which is red as well as some pink. This process is believed to be the same one that turns metal to a ruby red color when it rusts. The Granite may have some hematite grains within the feldspar leading to a more reddish outcome.
Like the black Granite, blue Granite doesn't exist. You may hear the name in the market but what you'll get is most likely larvikite. Based on the minerals and compounds that make up Granite, there isn't one that can turn to a blue color. It is therefore impossible to find a natural granite that's blue. Other types of rocks like larvikite and anorthosite are the ones with the blue mineral composition and are often passed around as Granite.
This is one of the hardest types of granites to distinguish. On the one hand, it's a way to pass on marble as Granite, but on the other hand, green Granite can be formed from a different variety of feldspar. Known as amazonite, this type of feldspar is capable of cooling off to get a green color that can be part of granite formation. However, it is usually rare unlike the infusion of serpentine to marble to form the green color. It's advisable to be keen when purchasing Granite.
Additional Granite Fact
Granite is used in different industries ranging from antiquities to engineering. This is even though there have been some rumors about the rock being radioactive. It indeed has the ability to attract radioactive elements, but its composition doesn't make it radioactive. It has also been proven that it is one of the safest rocks suitable for use in every home.
The way Granite is formed, and the elements it is composed of is what makes it an intrusive rock and not an extrusive one. The formation of different types of Granite is one of the most interesting natural occurrences taking place underneath the surface. It's easy to confuse Granite with other types of intrusive rocks like gabbro, but it is very easy to differentiate it from extrusive rocks like basalt. Granite doesn't result from volcanic eruptions and is rarely found on the surface like extrusive rocks. If found on the surface, it will be in smaller particles.