Gypsum

Limestone is a sedimentary rock mainly composed of calcium carbonate (CaCO₃).
It is formed from the deposition of shells, coral, algae, and marine debris.
Limestone reacts with dilute hydrochloric acid (HCl) producing carbon dioxide gas.
It is the main raw material used in the manufacture of cement.
Limestone is also used in the iron and steel industry as a flux.
Marble is the metamorphic form of limestone.
Limestone is generally white, grey, or light brown in color.
It is used in the production of quicklime (CaO) and slaked lime (Ca(OH)₂).
Limestone helps in neutralizing acidic soils in agriculture.
The Great Limestone Belt of India is found in Andhra Pradesh, Rajasthan, Madhya Pradesh, and Chhattisgarh.
Chalk is a soft and porous variety of limestone.
Limestone is used in glass-making industries.
Limestone is an important building material.
Karst topography (caves, sinkholes) is formed mainly in limestone regions.
Limestone is widely used in paper, paint, and chemical industries.
The presence of limestone indicates past marine conditions.

chemical formula = calcium sulfate dihydrate (CaSO₄·2H₂O).
Gypsum has a Mohs hardness of 2, so it can be scratched with a fingernail.
It is generally white, colorless, or gray
Gypsum is formed by the evaporation of saline water.
It is a sedimentary mineral.
Gypsum is used for making plaster of Paris (POP).
- When gypsum is heated to about 120–180°C, it forms plaster of Paris (CaSO₄·½H₂O).
Gypsum is widely used in the cement industry as a setting retarder.
- It slows down the setting time of cement caused by tricalcium aluminate (C3A)
It is used in fertilizers to improve soil structure and supply calcium and sulfur.
Gypsum is used in making wallboards, drywall, and false ceilings.
Gypsum crystals are commonly found in tabular or fibrous forms.
Alabaster is a fine-grained variety of gypsum.
Gypsum does not expand or shrink much on drying, making it useful in molds.