Which statement correctly describes the relationship between limestone and chalk?

Which statement correctly describes the relationship between limestone and chalk?

• A. All chalk is limestone, but not all limestone is chalk.
• B. Chalk and limestone are completely unrelated.
• C. Limestone is derived from chalk.
• D. All limestone is chalk.

Answer: (A)

Chalk is a specific type of limestone. Both are made primarily of calcium carbonate, but chalk forms from the fine, microcrystalline calcite that accumulates from tiny marine organisms, giving it a soft, white appearance. Because chalk is a form of limestone, every chalk rock is limestone. Yet limestone includes many other varieties beyond chalk—crystalline limestone, fossiliferous limestone, and others—so not all limestone is chalk. That makes the statement that all chalk is limestone, but not all limestone is chalk the best description. The other options misstate the relationship: chalk is not completely unrelated to limestone, nor is limestone derived from chalk, and not all limestone is chalk.

Chalk is a specific type of limestone. Both are made primarily of calcium carbonate, but chalk forms from the fine, microcrystalline calcite that accumulates from tiny marine organisms, giving it a soft, white appearance. Because chalk is a form of limestone, every chalk rock is limestone. Yet limestone includes many other varieties beyond chalk—crystalline limestone, fossiliferous limestone, and others—so not all limestone is chalk. That makes the statement that all chalk is limestone, but not all limestone is chalk the best description. The other options misstate the relationship: chalk is not completely unrelated to limestone, nor is limestone derived from chalk, and not all limestone is chalk.