The Delaware Coast

A layer of black sand is often seen on the beach after storms. Although it's surprising to see black sand beaches along Delaware's coast, it's not too unusual. This black beach covering is an accumulation of dark sand grains which are more difficult for winds and waves to move than the lighter colored quartz sand. Along Delaware's shoreline, the dark sands typically consist of heavy iron-rich minerals such as magnetite and illmenite; garnet, tourmaline and hornblende are another minerals commonly found in the dark sand mix.

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Question of the Month - January, 2003 Why do I occasionally see black sand on the beach? Topic: Heavy Minerals
	A layer of black sand is often seen on the beach after storms. Although it's surprising to see black sand beaches along Delaware's coast, it's not too unusual. This black beach covering is an accumulation of dark sand grains which are more difficult for winds and waves to move than the lighter colored quartz sand. Along Delaware's shoreline, the dark sands typically consist of heavy iron-rich minerals such as magnetite and illmenite; garnet, tourmaline and hornblende are another minerals commonly found in the dark sand mix.
These heavy minerals have a smaller grain size or diameter, but a greater specific gravity or density when compared to the white quartz sand. These characteristics result in a different hydraulic behavior from quartz grains and therefore these heavy minerals are often concentrated by waves and currents to form dark layers within the beach sand. Black sand deposits are often "left behind" as a lag layer during high wave conditions of winter, when the quartz-rich sand is preferentially transported alongshore or offshore.
	The next time you encounter a layer of black sand on the beach surface, take a small portion in your hand for closer examination. The sand grains are usually very small and are likely to stick to your hand and under your nails. Compare them to the typical white/tan sand from Delaware's beaches; observe differences in shape, grain size and color. Excavation of a small trench in the beach may reveal isolated layers of dark sand within the white layer-cake beach deposits, depicting a recent history of storm or high wave and wind events.
Please send in your suggestion for the “question of the month.” Questions and answers will be posted as the months unfold. For more information, contact Wendy Carey.

THIS MONTH AT THE DELAWARE COAST