Chalk is a porous limestone rock primarily composed of what compound?

Chalk is a porous limestone rock primarily composed of what compound?

• A. Calcium carbonate.
• B. Silica.
• C. Iron oxide.
• D. Magnesium sulfate.

Answer: (A)

Chalk is a porous limestone rock formed mainly from calcium carbonate, in the mineral form calcite (CaCO3). This composition comes from the accumulation of microscopic marine shells and organic debris rich in calcite, producing a soft, white rock with many tiny pores. The other substances don’t fit: silica (SiO2) would point to quartz-rich rocks, iron oxide would give a reddish color and isn’t the main material, and magnesium sulfate is a soluble salt, not a rock constituent. So the primary constituent is calcium carbonate.

Chalk is a porous limestone rock formed mainly from calcium carbonate, in the mineral form calcite (CaCO3). This composition comes from the accumulation of microscopic marine shells and organic debris rich in calcite, producing a soft, white rock with many tiny pores. The other substances don’t fit: silica (SiO2) would point to quartz-rich rocks, iron oxide would give a reddish color and isn’t the main material, and magnesium sulfate is a soluble salt, not a rock constituent. So the primary constituent is calcium carbonate.