The term 'Pleasant-sounding rock' can be answered with the 6-letter word 'Gneiss'. Gneiss is a type of metamorphic rock that is formed from the recrystallization of existing rocks due to extreme pressure and heat. It is characterized by its banded appearance, which is caused by the different minerals that make up the rock. Gneiss is often used in construction and is known for its pleasant sound when struck.