Granite countertops are a favourite among homeowners for many reasons. The most significant is arguably their wide range of natural patterns and brilliant colours which enhance your home’s beauty.
But have you ever wondered how those patterns and colours are formed? Let’s learn how.
Granite: The Formation of Its Colours and Patterns
Granite is mined from all continents. Composed of several minerals fused together under high pressure below the earth’s crust, it’s solid and highly durable. The word “granite” is derived from the Latin word for grain (“granum”) because there are visible grains of minerals on its surface.
Granite is mainly composed of quartz, alkali feldspars, plagioclase feldspars, and mineral impurities present during its formation. Feldspars in particular are easily affected by weather and exposure to ground fluids due to their chemical instability, which dramatically alters their appearance. (They can even change into completely different forms like clay minerals, bauxite and limonite.) The presence of quartz and feldspar along with the weathering effects produce the variety of colours we see in granite today.
The most common colours of granite are white, pink, yellow, grey and black, mainly because of its composition. Quartz is milky white, feldspar is white, potassium feldspar is pink, biotite is black or brown, muscovite is yellow, and amphibole is green. These minerals determine the colour of the granite depending on the type and ratio of their combination and external pressure. For example, granite with large quantities of potassium feldspar will look pink while large quantities of amphiboles make it look green. The presence of amethyst can tint it a faint purple while radiation can tint it a smoky to black shade. If it has a lot of quartz and amphibole, you will see the typical speckled black and white granite most commonly used in kitchen countertops.
Quartz and feldspar are key minerals in granite, comprising between 20% and 60% and 10% to 65%, respectively. Other minerals are amphiboles and biotite or muscovite (between 5% and 15%). These will determine the colour of the granite as well as its durability. As a rule of thumb, the higher the percentage of quartz, the harder the granite.
Below are some of the most popular granite colours and a brief description of each.
Traditional White Granite
White granite is made of milky white quartz and white feldspar. White granite forms because the conditions or pressure did not favour the formation of more amphiboles, or there simply weren’t other minerals present in the source material. The dark streaks or specks that you find in white granite are mostly amphibole. It’s extremely rare and almost impossible to find granite that’s solid white. If you do see one, it’s probably an engineered stone, not natural.
Classic Black Granite
Like white granite, black granite is rarely 100% black. If you do find one, it probably has a large percentage of biotite. However, granite with less than 20% quartz is more likely to be gabbro; this is an intrusive rock that features similar properties (if not composition) to granite.
Blush Pink Granite
As mentioned, pink granite contains a large proportion of potassium feldspar. It will also consist of milky white quartz, dark amphiboles, and white feldspar minerals.
Bold Red Granite
Red granite shares a similar composition with pink granite, except that the potassium feldspar has a darker shade. The red colour may also be the result of feldspar combined with iron oxide.
Cool Blue Granite
Although blue granite is popular among today’s homeowners, it’s unlikely to be true granite. Instead, it’s usually a type of igneous rock called monzonite, which contains less than 5% quartz, or anorthosite, also an igneous rock composed mostly of a feldspar mineral called blue labradorite. Although beautiful, it‘s not true granite.
Lush Green Granite
Green granite has a mixed dark and light green background with white specks on it. It typically contains a green feldspar mineral called amazonite. In most cases, green granite is a type of metamorphic rock with an abundance of marble or other types of rock, such as soapstone.
Granite countertops are preferred for their beauty, versatility and ease of maintenance. No matter what colour you choose for your countertop, proper care and use of a sealant are a must because leaving spills and messes can tarnish its surface. This will help retain its beauty and functionality for many years.