Properties of Kinds of Granite

Hardness

• Of the building stones, granite is the hardest. This is why it is one of the most popular stones used in creating countertops, because it can withstand hard force and a variety of elements. The hardness of a stone is measured according to the Moh's Scale of Relative Hardness, and granite, which is typically composed of the minerals feldspar and quartz, rates at about six or seven on a scale of one to 10.

Porosity/Permeability

• Porosity measures the ratio of pores in a stone. Granite's porosity ratio is quite low, typically at about 0.4 to 1.5 percent, and so it tends to have a fracture system rather than a pore system. This is where permeability comes in. Permeability measures how the pores and fractures of a stone interconnect to create a "flood system" -- that is to say, how liquids, moisture and vapors might be able to permeate the stone. Granite has an absorption percentage of between 0.2 to 0.5, which means that although its fracture system is more prominent than its porosity, it is still on the lower level of absorbent stones.

Thermal Stability

• Some stones are affected by their surroundings and change temperature to match the temperature of their location. This is where granite is unique. Granite is very thermally stable, meaning that it is not affected by its surroundings. Whether it be a drastic change in heat or cold, granite resists erosion due to temperature. Granite's ability to resist temperature change is also an indicator of another property of the rock that makes it a popular building material -- it is impervious to chemical erosion and staining.

Variegation

• Variegation means the coloration of a particular stone. A particular stone might be one solid color always or might be found in a range of several different colors, depending upon its makeup. Granite's primary composition of feldspar and quartz, with small amounts of other minerals mixed in, leaves granite with a fairly stable coloration and consistent texture, making the variegation of granite predictable.