Generally, granite with a rough surface is less pure than smoother granite.
Granite is one of the most important, tough and heat-resistant rocks used in building. It is also plentiful. In its pure form, granite is used in building tunnels and all manners of infrastructure. Its heat-resistant qualities make it indispensable in such areas as making steel and constructing hole fireplaces. Granite must be used in its pure form. Impurities in the rock make it more brittle than pure granite and prone to pockmarks. Depending on its level of purity, impure granite is basically useless. Does this Spark an idea?
Impure granite, from a practical and non-scientific point of view, usually looks very rough and is often weathered. Pure granite does not weather easily. Impure granite looks very diverse in its composition; its surface has many colors and different textures. The purer granite is, the smoother its surface is and the less colorful it appears. Using impure granite in construction can lead to structural breakdown. Identifying granite’s purity is very important before construction using granite begins.
Old geology journals and texts use the term “mafic” to describe an ingredient in impure granite. “Mafic” means containing iron and magnesium. The more mafic the granite, the less useful it is for science, building and heat absorption. One of the most important ways to define impure granite is to measure its iron content. Magnesium content also harms the general chemical structure of the rock, lessening its integrity and making it physically weaker.
“Porphyroblast” refers to a rock that contains crystals that grew far larger than normal. Under extreme circumstances underground, such as extreme heat or pressure, granite under formation might be forced to grow porphyroblasts. The disproportionately large crystals break down the granite’s integrity. They are often quartz and, under certain circumstances, can break down the feldspar that is a normal constituent of granite. Most feldspar, which composes about 60 percent of Earth’s crust, is very heat-resistant. Granite with little feldspar is less useful than granite with more feldspar.
Impure granite also contains what geologists call a “pronounced gneissic structure.” That means the rock’s mafic structure is significant enough to harm the rock’s integrity, and it shows itself in bands that give impure granite its uneven texture. The gneissic structure results from impurities such as iron that harm granite’s chemical integrity.