Why is marble harder than chalk and limestone Kid?

Marble is harder than chalk and limestone because it is a metamorphic rock formed from the intense heat and pressure of limestone over time. This process causes the minerals in marble to recrystallize, resulting in a denser and more durable structure. In contrast, chalk is a softer sedimentary rock made primarily of tiny fossilized shells, while limestone, although harder than chalk, is still less compact than marble. Therefore, the geological processes that create marble give it superior hardness.