Difference Between

Gypsum vs Limestone
 

Calcium and gypsum are minerals formed from calcium salts. But their properties and usages are different.

Gypsum

Gypsum is a hydrated calcium sulfate mineral with the molecular formula CaSO₄·2H₂O. This is the most common sulfate mineral.  It is a rock forming mineral that can grow up to very large sizes. Usually, the color of the crystal is white or colorless, but can have other shades of color as grey, red or yellow too. Also, crystals can be transparent or translucent. Gypsum is a soft crystal which even can be scratched by a fingernail. Further, it is flexible and thermal conductivity is low. Gypsum is abundant in Colorado and Mexico in USA. Gypsum is mainly formed from precipitation of marine water. While forming, other mineral types, water or unwanted material can trap inside the crystal, which is the cause of different colored crystals. This is widely used for making plaster of Paris, some cements, fertilizer and as an ornamental stone.

Limestone

Limestone is commonly found in marine environments, and they are classified as sedimentary rocks. These are mainly formed in shallow, warm and calm waters. Biological activity also plays an important role in forming limestone. Normally, they are formed in waters where carbon dioxide concentration is low so that the sedimentation is quite easy. Marine water receives calcium from land, and there is a lot of calcium carbonate containing materials, such as shells of mollusks and other sea animals, coral, skeletal structures of sea animals, etc. When these are accumulated in the form of calcite (other waste materials also tend to incorporate into this when accumulating), they are known as limestone. They are also categorized as biological sedimentary rocks. There is another type of limestone known as chemical sedimentary rocks. They are formed by direct precipitation of calcium carbonate in sea water. However, the biological sedimentary rocks are more abundant than chemical sedimentary rocks. In pure limestone, there is calcite only, but often they can contain impurities by mixing other materials like sand. So, limestone can be defined as a sedimentary rock, containing more than 50% of calcium carbonate in the form of calcite. Other than in oceans and seas, limestone can be formed in lakes or other water bodies with necessary conditions. In the world, limestone formation can be seen in Caribbean Sea, Indian Ocean, Persian Gulf, Gulf of Mexico, around Pacific Ocean islands, etc.

The nature of limestone depends on how it is formed. They can be in massive sizes, crystalline, granular, etc. They are classified into several groups according to their type of formation, composition or appearance. There are many classifications too. Some of the common limestones are chalk, coquina, lithographic limestone, oolitic limestone, fossiliferous limestone, tufa, etc. there are many usages of limestone too. They are commonly used as an ingredient for cement and glass manufacturing, hence an essential construction material.  Since, limestone has a basic nature; it is used to neutralize acidic water bodies.