Granite weighs approximately 2.75 grams per cubic centimeter, which is 2,750 kilograms per cubic meter. It is composed of slightly less than three-fourths silicon dioxide and roughly one-seventh aluminum oxide. The rest consists of other oxides, such as potassium oxide.
Granite is slightly heavier than pure silica sand and quartz, which, as forms of silicon dioxide, weigh 2.648 grams per cubic centimeter. While it is roughly the same weight as most other igneous rocks, it weighs less than the 2.9 grams per cubic centimeter of basalt. Granite is not composed of exact proportions of minerals, and tens of thousands of granite types exist. The more quartz is in granite, the less it weighs; the other oxides, which naturally occur as the mica and feldspar in granite, weigh more.
The weight of granite makes it a concern for home use. Granite countertops are only, at most, 4 centimeters thick, and the cabinet underneath must be reinforced to support its weight. A counter entirely made of solid granite would need structural support or risk collapsing through the floor.
While some granites contain heavy, naturally occurring uranium, the 10 to 20 parts per million do not noticeably affect the overall weight of granite.