Rocks can be used many ways in the landscape--as mulch, for walkways and borders, or as accent pieces. The type and color of rocks should complement the style of the landscape. Landscape rocks, especially the smaller sizes, should be laid on water-permeable landscape cloth to prevent them from sinking into the ground.
Gravel is small pieces of broken stone. The smallest, pea gravel, consists of pieces that measure 3/8 inch and smaller. Gravel up to 1 inch can be used for pathways, patios and garden beds. Larger gravel is primarily used in garden beds.
River rocks have been worn down by the movement of water for a smooth, rounded finish. They are available in several sizes and colors, including gray, tan and pink. They can be used in garden beds or to create a dry creek bed.
Black lava rock is actually grayish green to dark black. Lava rock is also available in red. Smaller pieces--up to 1 inch--can be used in garden beds and walkways. Larger lava rock can also be used in garden beds and in driveways. Lava rock boulders can be used as accent pieces in garden beds or as mass groupings in a landscape.
Fieldstone is found stone that is left uncut. Rubble stone is usually basalt, granite or gneiss left uncut for stepping stones and walls. Boulders of different types of stone can be used in a group or singly to highlight an area of the landscape.
Flagstones are shallow flat slabs of granite, limestone or sandstone used for walks, patios and walls. Ashlar blocks are cut out of granite, limestone or sandstone in geometric shapes with straight edges for building walls. Belgian blocks are about the size of bricks, and are cut from granite or some other durable stone.