Which term describes the chemical alteration of rocks due to introduction of external materials such as fluids or melts?

• A. Metasomatism
• B. Metamorphic Rock
• C. Mantle Keels
• D. Pipe

Answer: (A)

Metasomatism is the chemical alteration of rocks caused by the introduction of external materials such as fluids or melts. When hot fluids or silicate melts move through a rock, they transfer ions and elements, causing minerals to dissolve and new minerals to crystallize. This changes both the mineralogy and the chemical composition of the rock, often along fractures or near igneous intrusions where these fluids are most active.

This differs from simply metamorphosing a rock through pressure and temperature, which reshapes minerals without a substantial addition or removal of chemical components from outside the rock. It’s also not describing a rock type or a structural feature like a mantle keel or a pipe.