Black sand beaches can be made up of two different types of sand. One is made by placer deposits and is composed of a heavy, glassy mixture of fine sands. This type of sand is also partially magnetic. The second type of sand is made of smaller fragments of lava and is generally found in close proximity to volcanoes.
Black beaches are formed when the lava particles are separated from normal sedimentary rock and deposited on beaches near volcanoes. This type of formation leaves a heavy concentration of minerals, and these deposits have also been known to hold precious gems which are mined from these black sand beaches.
Black sand beaches can be formed by the Earth's weather patterns causing lava to erode into the sandy beaches. The tides help break up the lava that rests on the shallow ocean floor -- turning it into a fine sandy material -- and then will redeposit the sand on the beach. It is a common occurrence to see steam explosions when the hot lava meets up with the cooler waters.
Though black sand beaches are a rare occurrence throughout the world, there are several regions where they are common. Islands that have black sand beaches include Iceland, Hawaii, Indonesia and Polynesia. There are some islands in the Caribbean which also have black sand beaches, such as Dominica, St. Lucia, St. Vincent, Granada and Puerto Rico.
