The key difference between gypsum and limestone is that the calcium sulfate is the main constituent in gypsum whereas calcium carbonate is the main constituent of limestone.
Limestone and gypsum are minerals that form from calcium salts; limestone contains calcium carbonate while gypsum contains CaSO4·2H2O. However, their properties and usages are different from each other.
What is Gypsum?
Gypsum is a hydrated calcium sulfate mineral with the molecular formula CaSO4·2H2O. It is the most common sulfate mineral. Moreover, it is a rock-forming mineral that can grow up to very large sizes. Usually, the colour of the crystal is white or colourless but can have other shades of colour like grey, red or yellow too.
Also, crystals can be transparent or translucent. Gypsum is a soft crystal which we can easily scratch by a fingernail. Further, it is flexible and thermal conductivity is low. Gypsum is abundant in Colorado and Mexico in the USA. Gypsum mainly forms from precipitation of marine water. There, while forming, other mineral types, water or unwanted material can trap inside the crystal, which is the cause of different coloured crystals. We use this material often to make plaster of Paris, some cement, fertilizer and as an ornamental stone.
What is Limestone?
We can find limestone commonly in marine environments, and we can classify them as sedimentary rocks. Furthermore, this material mainly forms in shallow, warm and calm waters. Also, biological activity plays an important role in forming this material.
Usually, they form in waters where carbon dioxide concentration is low; thus, 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 materials accumulate in the form of calcite (other waste materials also tend to incorporate into this when accumulating), we call it as limestone.
Moreover, there is another type of limestone; chemical sedimentary rocks. They form via direct precipitation of calcium carbonate in seawater. 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 such as sand. Therefore, limestone is a sedimentary rock containing more than 50% of calcium carbonate in the form of calcite.
Further, other than in oceans and seas, limestone forms in lakes or other water bodies with necessary conditions. In the world, we can observe the limestone formation in the Caribbean Sea, Indian Ocean, Persian Gulf, Gulf of Mexico, around Pacific Ocean islands, etc.
Nature and Uses
The nature of limestone depends on how it forms. They can occur in massive sizes, crystalline, granular, etc. We can classify them 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.
Moreover, there are many usages of limestone too. We commonly use them 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.
What is the Difference Between Gypsum and Limestone?
Gypsum is a hydrated calcium sulfate mineral with the molecular formula CaSO4·2H2O and limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral and mollusks. Therefore, the key difference between gypsum and limestone is that calcium sulfate is the main constituent in gypsum whereas calcium carbonate is the main constituent of limestone.
Moreover, gypsum is more soluble than limestone. As another important difference between gypsum and limestone, limestone is an acidic mineral. It can change the soil pH due to the carbonate group, but gypsum is a neutral mineral; therefore, it cannot change soil pH. Furthermore, gypsum can grow into larger crystals than limestone.
The below illustration provides more details on the difference between gypsum and limestone.
Summary – Gypsum vs Limestone
Gypsum and limestone are calcium salts. The key difference between gypsum and limestone is that calcium sulfate is the main constituent in gypsum whereas calcium carbonate is the main constituent of limestone.