Marble is a metamorphic rock

Metamorphic rock

Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 composed of recrystallized carbonate minerals, most commonly calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

 or dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

.

Geologists use the term "marble" to refer to metamorphosed limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.

Marble is commonly used for sculpture

Marble sculpture

Marble sculpture is the art of creating three-dimensional forms from marble. Sculpture is among the oldest of the arts. Even before painting cave walls, early humans fashioned shapes from stone. From these beginnings, artifacts have evolved to their current complexity...

 and as a building

Architecture

Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...

 material.
The word "marble" derives from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 "" (mármaron), from "" (mármaros), "crystalline rock", "shining stone", perhaps from the verb "" (marmaírō), "to flash, sparkle, gleam".