Every countertop you see is not granite. Or... is it?
If you read my post “Countertop Talks Part 1”, you would know that the answer to the above question is “probably not”. If you have not read that article yet, I highly recommend reading Part 1 first to get familiar with the names of some of the stone types we will touch on in this article. Either way, knowing how these different stones form in nature helps us understand their properties, similarities, and differences, and appreciate the forces of nature a little more.
The Origins of Rocks
On a very high level, there are three types of stones or rocks namely Igneous rocks, Sedimentary rocks, and Metamorphic rocks.
Igneous rocks are formed from cooled magma either on land or in underwater magma chambers under extreme conditions of temperature and pressure.
Sedimentary rocks on the other hand form through the process of sedimentation which involves the deposition and compacting of sand, clay, and other minerals over time. This process can happen on land, meaning on beaches, deserts, or even on rivers and ocean floors.
Finally, we have Metamorphic rocks which as the name suggests form through the metamorphosis of stone! This process of metamorphosis takes millions of years and occurs under extreme environments of temperature and pressure.
I am not a geologist by any measure so, if you would like to geek out and learn more about the origins of rocks, check out this article written by a Geologist: Geology of Natural Stone
So, what type of rock is granite?
The short answer is Granite is an Igneous rock.
But now that you know the types of rocks and have an overview of how they form, would you not like to know if you really have Granite at home? Or if it is one of those other 'Granites' like Gneiss, or Schist?
I knew you would be interested so here we go.
Let us start with Schist – Schist is a Metamorphic rock meaning it became Schist from a different type of rock which in this case is Slate. Slate itself is a metamorphic rock formed from Shale which is just compressed clay. When the slate is subjected to extreme conditions of temperature and pressure, the clay in the rock turns into Mica which is a silvery and shiny mineral that when subjected to more heat and pressure, turns into Schist. The schist as a rock is extremely hard and shiny. It is also usually non-porous and resistant to etching meaning most day-to-day acids like lemon juice and tomato juice will not affect this rock.
Let us move on to Gneiss now – This is also a metamorphic rock. Any guesses on what the parent rock is? It is Schist! Yes. When Schist is subjected to further heat and pressure, an odd thing happens – the light and dark minerals in the Schist start to separate and this separation of minerals is seen in the form of waves or pools in the rock. At this stage when the waves are formed, the rock is Gneiss and the waves are a giveaway that the rock is actually a Gneiss. You will also notice some really cool minerals in the rock like Garnets which are burgundy in color and round. Gneiss is again a very hard rock like its parent rock but not shiny anymore. Gneiss like Schist is also usually non-porous, resistant to etching.
When Gneiss is further subjected to heat and pressure, it melts! Yes, rocks melt too! This molten rock is what we call magma. Yikes! We think our lives are hard – just imagine what these poor rocks are going through. That is a painful lifecycle with no exits!
Jokes aside, it is now time to let the star of the show, an igneous rock, take center stage! Welcome Granite.
If you paid attention to the different types of rocks and how they are formed above, you would know by now that igneous rocks form from cooled magma, so to put it simply Gneiss turns into Magma which then cools into Granite. As you would expect, Granites are extremely hard, scratch-resistant, etch-resistant, and non-porous most of the time.
As you can see by now, these different types of rocks share some very similar properties which have contributed to grouping these rocks and many more Igneous rocks into the Granite category.
However, notice how I said most of the time above. This is because not all the properties are true for all types of Granite or any rock type for that matter. While most Granites, Schists, and Gneiss truly are very low maintenance and non-porous, I have come across true granites that do absorb liquids and turn darker. I have also come across issues where the minerals in the rocks have reacted with chemicals used to treat the rock and change the color of the rock. While most of these issues are reversible, it is important to note that not all rocks are made equal in nature.
To Summarize
In nature, rocks go through extreme environments during their formation and depending on where the rock is in its lifecycle at the time of extraction, the properties of these natural rocks will vary no matter which type of rock it is classified as. To make it a little more fun, some rocks are an amalgamation of two or more rock types. What is not to love about nature's whimsy? :D
Have countertop questions? Confused about which countertop is best? Hit me up! I love talking about countertops and I am very happy to help. :)
Check out the other posts on the origins of different stones like Part 3 on Quartzites, Part 4 on Marbles, Part 5 on Travertine, Part 6 on Onyx, and Part 7 on Soapstone, and don't forget to subscribe to my Newsletter at bottom of this page to be notified when new posts are published.
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