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A group of minerals containing various amounts of the elements Silicon and Oxygen. The Silicates are the largest group of minerals. The construction component of all Silicates is the tetrahedron, which is one Silicon atom equidimensionally placed around four Oxygen atoms.
Glass is made of silicon. The only mineral made up exclusively by silicon is quartz, which is also the main mineral in common sand. So the answer is quartz, but you're not wrong thinking sand, only sand is not a mineral.