Which silicate mineral is commonly a potassium-bearing mineral and a major component of feldspar?

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

Answer: (C)

Feldspar is the mineral group that fits both clues: it is a major rock-forming silicate family, and within that group there are potassium-bearing varieties (potassium feldspars such as orthoclase, microcline, and sanidine). These potassium-rich members are common in a wide range of rocks, making feldspar a dominant component of Earth’s crust.

Quartz is also a silicate, but it doesn’t include potassium in its structure. Muscovite is a potassium-containing mica, not a member of the feldspar family, so it isn’t described as a major component of feldspar. Calcite is a carbonate mineral, not a silicate, so it doesn’t fit either.