There is none. Billiard balls are made from a synthetic material using a resin that is either phenolic or polyester based.
A core phenolic center is made that is not of high tolerance. Then, at least 2 additional layers are built up over the core, each of better tolerance. In most cases, only the outer layer has the color and design. The exact material, method and number of layers varies from type to type. There is a reason one set may cost $160 and another only $60, and it generally is assocaited with the effort and tolerance.
metamorphic
Any type of rock can become metamorphic.
metamorphic.
slate
Schistose Structure metamorphic rocks are known as foliated metamorphic rock.
A metamorphic rock.
metamorphic
It is a type of Metamorphic rock
it is a non foliated metamorphic texture.
Metamorphic has this root.
Any type of rock can become metamorphic.