Decomposed granite is one kind of material used as a construction aggregate. Decomposed granite is usually obtained from weathered stone sources and then is mechanically crushed to form a course gravel-like consistency. Other than being used as an aggregate, decomposed granite is also used for laying paths, or as a mulch for gardens. It can be laid loosely, packed down or secured with epoxies to create an asphalt-like covering.
Sand is one of the most commonly quarried construction aggregates and is one of the two natural aggregates. Sand is usually sorted by coarseness and color. Like decomposed granite, sand can be used not only as an aggregate, but for laying paths. It's also used on artificial beaches and in sandboxes for children.
Gravel is another natural construction aggregate. Because it is mined as is, it does not need any further processing and is therefore cheaper than decomposed granite. Instead of being crushed to size, gravel is sorted into different grades. The grade with natural aggregates is not as consistent, however, as it is with crushed stone.
Shale is sometimes used as a lightweight construction aggregate. Shale and clay make up nearly 80 percent of the Earth's crust, so they are easily found. Shale, however, is easily eroded and becomes clay or mud with extended exposure to weather. Some shale has a large amount of organic matter, so much so that a thin sliver of them can be set on fire with a match. After heating, shale will often take on a red color.
A great reuse of old concrete is as a construction aggregate. It saves money on both sides of the process, the cost of disposing of concrete at a landfill and the purchase of new aggregate from a quarry. Like decomposed granite, recycled concrete can be crushed to a consistent grade. It's a green alternative to mining and transporting new aggregate, and while concrete is not considered to be environmentally damaging, the amount of concrete waste cannot always be accommodated by landfills.