Natural gravel originates from beaches or banks of rivers that have not turned into solid rock. For example, ancient beaches such as from the Jurassic Era are dug up in quarries.
This material is sifted into different groups based on the size of the gravel. It is then sold to companies for use in building, landscaping, etc.
Most natural gravel or sand is made of silica which is very durable.
Some gravel materials are originally hard rock. This must first be crushed into granite or limestone gravel.
Gravel is rock particles larger than 1/12 of an inch and no more that 2.5 in. Small gravel is made of granules while large gravel are referred to as pebbles. Any particles smaller that 1/12 of an inch are considered to be sand and larger particles are cobbles.
The most common sizes of gravel used is 2.5 inches and 1 inch.
Both gravel and sand are used for cement, tarmac and road surfaces. Mixtures of sand and gravel with other various crushed materials are called aggregate. These mixtures are usually used for drainage.
Gravel is also used for decorative purposes in landscaping, railroads, walkways. It needs maintenance both as paved roads and unpaved gravel roads in order to control dust, extend lifespan, and to make sure that operations stay in top shape.
Throughout the U.S., there are more than a million miles of unpaved road, most of which is made with some form of gravel. Gravel is an important part of the infrastructure of modern society as it is used in building of all kinds.