How could marble become an igneous rock?

Simple: completely melt the marble, such as by exposure to magma, then recrystallize it into igneous rock without subsequent deformation or significant weathering. It will no longer be marble, however, since that is a metamorphic rock. read more

i almost said it could not be an igneous rock ecause there was no igneous rock defined as. being primarily calcium carbonate. But then wisdom overcame ego and I called a friend who said the igneous rock carbonatite is mostly calcium carbonate with a few other mineral thrown in. read more

Marble is a metamorphic rock, but it can never be guaranteed that marble will never become igneous rock again. Assuming tectonic conditions leading to burial of a marble rock deep inside the Earth where it melts under high temperature and pressure, it can form magma which can eventually cool down and crystallise to igneous rock. read more

Once its molten it is called magma (assuming its below the Earth's surface) and when it cools it becomes an igneous rock. Assuming the molten marble is not assimiliated with silica-rich magma before it crystallizes, it would be called a carbonatite. read more

Limestone is a sedimentary rock composed of the mineral calcite, which in turn is made up of calcium carbonate (CaCO3). When exposed to heat and pressure the rock recrystallizes but the chemical composition does not change. read more