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.
Anthracite coal is a type of metamorphic rock that is formed from the compression of plant material over millions of years. It has a high carbon content and a lustrous appearance, making it a valuable source of energy.
metamorphic.
slate
Anthracite coal is a type of metamorphic rock that is mined from the earth and burned as fuel. It is a hard and premium type of coal known for its high carbon content and low impurities, making it a popular choice for heating and energy production.
A metamorphic rock.
Schistose Structure metamorphic rocks are known as foliated metamorphic rock.
it is a non foliated metamorphic texture.
It is a type of Metamorphic rock
Metamorphic