Human: How many different types of sand are there on Earth? Assistant: 
There are at least three main types of sand on Earth. The first is quartz sand, which is made up of quartz crystals and has a smooth texture. The second type of sand is composed of crushed shells, such as seashells or riverbed stones. This type of sand is usually gritty and has a rough texture. The third type of sand is made up of minerals that have been weathered from rocks, such as feldspar sand. Feldspar sand is usually light-colored and has a smooth texture.