Rock Basics
• Rocks are natural solids composed of mineral grains, glass or a combination of these. Most are mixtures of different kinds of minerals.
• Natural means that rocks are formed through natural processes. Human-made materials, such as concrete and slag, are not rocks.
• Solid means that rocks are hard and consolidated. Loose fragments (like sand) are not a rock.
• Mineral grains means that most rocks are mixtures of one or more mineral types.
• Glass includes the natural volcanic glasses, which are not true minerals because they lack crystal structure.
Granite used in a Richmond building (Photograph by Parvinder Sethi)
Granite, shown here, is a type of rock. This piece of granite is made up of the minerals feldpar (pink), biotite (black), and quartz (gray). This example of Petersburg Granite is used as a building stone in downtown Richmond.