Flagstone can be made from different varieties of rock. A flagstone is made of natural rock -- usually sedimentary stones such as limestone or sandstone -- and is usually about one to two inches (2.5 to 5.1 centimeters) thick [sources: First, Walks, Walls & Patios]. "Flagstone, by definition for us, is material that is tough enough to stand up to the outdoors for a long period of time," says First. "It's relatively thin and flat so that it can be walked on and fairly easily installed."
The slab-like quality of flagstone makes it a good fit for many different areas of the yard. "Flagstones are used most often for paths, patios, stair treads and wall coping," says Pulver.
Flagstones can be irregularly shaped or more uniformly shaped into squares or rectangles depending on your preference. The uniformly shaped versions offer the possibility of a pattern to add a formality or decorative touch to the area you're creating.
Along with style, you have to think about functionality when choosing the right stone for your application. When choosing flagstone for a walking surface, be sure to think about how slick the surface might get when wet; choosing something with a little more texture might help with traction [source: Pulver].