What mineral is the major constituent of sandstone and other clastic sedimentary rocks?

• A. Feldspar
• B. Calcite
• C. Quartz
• D. Silica

Answer: (C)

Quartz is the mineral that most commonly makes up sand-sized grains in sandstone and other clastic rocks because it is chemically very stable at Earth's surface and highly resistant to weathering. When rocks break down, different minerals weather at different rates: feldspar tends to transform into clay minerals, and calcite dissolves in slightly acidic water. Quartz survives long transport by wind or water, remains hard and resistant to abrasion, and thus remains as the dominant grain in sandstones. In petrography, quartz is the specific mineral name to identify this dominant component; “silica” refers to SiO2 in a broader sense, but the mineral most commonly forming the sand grains is quartz.