Decomposed granite, sometimes referred to as DG, is most commonly recognized as a building and landscape material. It is popular in the construction of trails, parking areas, and roads, as well as in backyard landscaping. Decomposed granite consists of weathered granitic particles that range from gravel to silt size, and usually include some clay. The name of decomposed granite refers to the fact that the particles are the result of natural weathering, or decomposition, of granite rock.
One of the most common places to find DG is in hiking trails. The materially is fairly stable when compressed, and yet remains a permeable material, allowing for satisfactory drainage. In addition to trails, decomposed granite is commonly used to construct driveways and parking areas. Decomposed granite is also sometimes used in road construction, although it must be compacted to form a firm driving surface.
Decomposed granite is popular in landscaping as a hardscape material. It can be used as groundcover, mulch, patio base, or for creating paths. Decomposed granite is a fairly environmentally friendly choice because it is a natural product, is permeable, and provides hardscape that requires no water. After the granite is in place, it will continue to weather, which adds beneficial nutrients to the surrounding soil and plants. Not surprisingly, decomposed granite is a particularly popular landscaping choice in arid regions.
Depending upon the climate and the intended use, DG can be used by itself with only moderate compression to keep it in place, or can be set in place with stabilizers. If the granite is being spread by itself, it is usually contained with some sort of border or framework to prevent the granite from washing away easily. In contrast, if the decomposed granite is being set with stabilizers or resins, the hardscape with be more permanent and stable, but the permeability will be reduced, making drainage an important consideration.
Decomposed granite usually refers only to granite that has weathered naturally, however, it is often discussed interchangeably with crushed gravel and crushed stone. Each of these products has angular pieces and usually a percentage of fine pieces. They are often used for similar types of construction or landscaping processes.
The formation of decomposed granite occurs over time, and is the natural result of weathering and erosion of granitic rocks. Wind and water both physically and chemically weather the granite, eventually fracturing the small pieces that make up decomposed granite. The final product is mined in granite quarries, usually alongside other granite products such as large boulders, slabs, and manufactured crushed granite.