Why is marble called a metamorphic rock?

Because it is. Marble was called marble before we knew how it formed. Once we learned how it formed, we knew that the rock called 'marble' was a metamorphic rock. read more

Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite (CaCO 3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite. read more

In the building industry, ANY calcite rock that is massive and looks pretty when polished is called ‘marble’, but some of it is actually just a nice massive limestone (Holston ‘Marble’ from Tennessee is a limestone, for instance). Limestone is a sedimentary rock, and marble is metamorphic rock formed from limestone. read more