The word “Granite” is used in a variety of different ways and is mainly used as a general consumer term for rocks that have visible grains and are harder than marble. For this reason, many different types of rocks that are not actually true granites are grouped together under the “granite” definition to avoid consumer confusion and simplify the description for sales purposes. You may hear the term “Dimensional Stone”, this means the stone has been cut into blocks or slabs of specific size and used for consumer purposes like counter tops.
There are several different methods in which rocks are formed, igneous, sedimentary and metamorphic. Granite is an igneous (Ig-knee-us) rock, there are two basic ways igneous rocks form, intrusive and extrusive. Intrusive granite is “True Granite”, it cools at a slow pace and usually has larger mineral crystals in it. Extrusive is also known as volcanic rock and is formed at the crusts surface. An extrusive rock cool and solidifies faster than intrusive rocks and usually has smaller, finer grain. A few examples of extrusive rocks are absolute black, basalt, and black galaxy.
Dimensional stone is grouped into two basic groups based on their mineral make up, calcareous and siliceous. Marble is under the calcareous group, and granite falls under the siliceous group. Silicate minerals make up the largest group of minerals that are found in dimensional stone. Silicate minerals are generally not acid sensitive, this is one of the reasons granite is so durable and resistant to etching and chemical damage.
The minerals that generally make granite is usually a blend of quartz, feldspar, micas, and several others. Granite gets its durability from these mineral make ups, as granites are mostly quartz and feldspar, their hardness is very high. In the Mohs Scale of Hardness, feldspar ranks 6 out of 10 and quartz ranks 7 out of 10! To give you an insight on how hard this is, your fingernail ranks a 2.5 and a steel knife or nail ranks only a 5.5!
The hardness and durability of granite is why we use specialty tools that are studded with diamonds. Our blades are not sharp to the touch as “cutting” is more of a grinding operation. Even our polishing pads are studded with diamonds to make grits from as low as 50 grit to 5000. Diamond is one of the hardest minerals known to man with a Mohs ranking of 10 out of 10!