White sand, for its picturesque quality and soft texture, is one of the most desirable types of sand for beaches. The purest white sand is gypsum sand, which can be found at White Sands National Monument in New Mexico, the world's largest gypsum dunefield. Most white sand, however, comes from eroded limestone, and can also derive its white color from quartz and coral deposits. Renowned white sand beaches include those on the island of Koh Chang in Thailand.
The yellow sand in beaches such as Mellieha, on the island of Malta, is primarily composed of silica formed from quartz crystals. Iron impurities in these crystals are what give yellow sand its distinctive range of hues, from dull yellow to tawny golden. Yellow sand tends to be coarser than white sand, ideal for packing sand castles and more resistant to being redeposited by the tide. It is also more inexpensive for landscapers to purchase than more highly prized white sand.
Black sand is often heavy in obsidian or basalt (rapidly cooled lava). The black color indicates that the sand contains a lot of magnetite, a mineral with natural magnetic properties. This allows landscapers to separate black sand from other types of sand by use of a magnet. Black sand is glossy and reflective of the hot sun. Beaches such as Waianapanapa Beach in Maui are renowned for their long, striking stretches of black sand.
Due to their rarity, green sand beaches are notable tourist destinations. The green color results from the gradual erosion of basalt, which yields olivine crystals that contain both iron and magnesium. These minerals make olivine sand particles relatively heavy, remaining on the beach after lighter varieties of silica have been washed away by the tide. Few beaches in the world are primarily composed of green sand, but vacationers can visit one on the island of Guam.
