Chalk and marble are different forms of

Chalk, limestone, and marble are all different physical forms of the chemical compound calcium carbonate (CaCO3) [2][3]. While they differ in their formation processes and physical appearances, they share the same chemical composition [1]. Chalk is a soft, porous sedimentary rock formed from the accumulation of microscopic marine shells [1]. Limestone is also a sedimentary rock, often derived from corals and shells [1]. Marble is a metamorphic rock formed when limestone undergoes intense heat and pressure [1][3]. Chemically, these substances consist primarily of calcium, carbon, and oxygen. They are characterized by their reaction with acids to produce carbon dioxide, water, and a corresponding salt [2]. Although calcium hydrogen carbonate exists in dissolved forms in water, the solid mineral forms found in rocks like chalk and marble are specifically calcium carbonate.

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Activity 2.5 > p. 21
2. [3] https://www.sciencedirect.com/topics/chemical-engineering/calcium-carbonate
3. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Limestone and Chalk > p. 76