WHAT IS SEDIMENT MADE OF? The vast majority of sediments that we encounter on Earth are silicon dioxide, quartz. The material of the continents is rich in silicon, so it is abundant in the breakdown of continental rocks. Basaltic rocks from the ocean floor are less common on dry land. These sediments derived from oceanic crusts would be found near areas of volcanic activity that brought this material onto the continent. Sediments can also be formed by salts. Salts can dissolve in water, and the vast majority of it makes its way to the ocean. In some places, such as the Caspian Sea, the centre