Complex sentence: The rocks of the Florida dyke swarm have been quarried since the 1960s and are used in the construction industry as black dimension stone of very high quality, being marketed as "black granite".
Split into simpler sentences: The rocks of the Florida dyke swarm have been quarried since the 1960s. These the Florida dyke swarm rocks are used in the construction industry as black dimension stone of very high quality and marketed as "black granite".