Marble is metamorphosed limestone, composed of very pure calcium carbonate, CaCO3. The softness of marble and its relative isotropy and homogeneity make marble very desirable for sculpture and building stone. Although marble comes from limestone, the temperatures and pressures necessary to form marble usually destroy any fossils that may have been present in the limestone.
In the building trades, the term "marble" is used for any massive, crystalline calcitic rock (and some non-calcitic rocks) useful for building stone. For example, Tennessee Marble is really a massive, highly fossiliferous gray to pink to maroon Ordovician dolostone, known as the Holston Formation by geologists.
Marble derives its name from the Greek marmaros, shining stone. [source: OED2]. This stem is also the basis for the English word marmoreal meaning "marble-like".
In folklore, marble is associated with the astrological sign of Gemini. Pure white marble is an emblem of purity. It is also an emblem of immortality, and an ensurer of success in education.