What Is Gypsum? Detailed Explanation for Chemistry Students
There are many minerals found in nature, and for the students of Chemistry, it is very important to learn about these minerals, and Gypsum is one of those minerals. Hence, it is necessary for the students of Chemistry to learn about the Gypsum in as much detail. But at the same time, students must have access to the explanation of the topic of Gypsum in a manner which they can easily understand, otherwise, it serves no purpose than to give the anxiety to the students which may ultimately lead to the students believing that the topic of Gypsum is difficult to understand and they are not in a position to do so.
Hence, to help the students of Chemistry in learning about the topic of Gypsum, Vedantu provides the complete explanation of the said topic in a language which they can easily understand because this explanation of the Gypsum is prepared by the top educators, who knows how to communicate the topic with the students in an effective manner. Therefore, they have prepared this explanation in an accessible language, so that students have a hassle-free experience.
Also, as said, Vedantu provides the complete explanation of the Gypsum, which mean it includes everything regarding the said topic, that is to say, the meaning of Gypsum, its background, places where it can be found, the chemical formula for the gypsum, various kinds of Gypsum and many more things. And if students still have some doubts in their mind, they can find the solution of the same from the section of Frequently Asked Questions (FAQs). And Vedantu provides this complete package of the Gypsum free to all the students.
An Overview of the Gypsum
Gypsum is the mineral that includes in its structure Sulfate ion, which makes it a sulfate mineral, and of all the sulfate minerals, Gypsum is the most common. Gypsum is composed of hydrated calcium sulfate, and its chemical formula is CaSO4.2H2O. It is a natural salt mineral, that is to say, an evaporite mineral, and is mostly found along with halite, sulphur, dolomite, anhydrite, and calcite. If we look at the chemical formula of Gypsum and Anhydrite, we can see that Gypsum is much similar to the Anhydrite, because as mentioned, the chemical formula of Gypsum is CaSO4.2H2O, while the chemical formula for the Anhydrite is CaSO4, the only difference between the two is that while Anhydrite contains no water, Gypsum contains two glasses of water.
Gypsum is a naturally occurring mineral composed of hydrated calcium sulfate and appears soft white or grey in colour. It is formed mainly in layered sedimentary deposits and has a variety of uses in many industries like building, sculpting, gardening, and ornaments. It is an inert and safe mineral that has existed for millions of years since you can find it being used in Egyptian pyramids as well. It is the most common sulfate mineral.
Occurrence of Gypsum
As said earlier, Gypsum occurs along with other minerals such as halite and anhydrite. These all are the evaporite minerals, and hence the gypsum. It means that Gypsum is the sedimentary deposit, that is to say, it is deposited by the action or the work of wind or the water, usually in the bottom of the water body. In particular, Sulfate is deposited from the natural brine that occurs in the ocean, which is then followed by anhydrite and halite.
In the saline lakes, that is to say, the salt lakes, and a salt pan, which means the area where the water has been evaporated and the salts and minerals are left behind (sulfate is found in those minerals). When the groundwaters and surface waters do hydration of anhydrite, it forms the gypsum, as a matter of fact, it is one of the common occurrences of the gypsum. In a widely dispersed manner, gypsum can also occur in limestones and dolomitic limestones.
Throughout the world, gypsum deposits occur in many countries, but Spain, the United State of America, Russia, Turkey, and Thailand are the top-most producers of Gypsum. Since gypsum is dissolved in the water over a period of time, only on rare occasions it can be found in the form of sand, and hence mostly it is found in the crystal form. The gypsum crystal of more than 3 metres or of almost 10 feet in length, and of 0.4 metres or almost about 1.5 feet in diameter, was found in the Braden mine of Chile. This particular crystal of the Gypsum is one of the largest crystals of gypsum ever found.
Where is Gypsum Found?
Gigantic gypsums are formed beneath layers of sedimentary rock, along with halite, anhydrite, sulfur, calcite, and dolomite. Thick beds and layers of rocks are commonplace for finding gypsum. Ocean water is high in calcium and sulfate minerals so gypsum is also found in lagoons as the water in the ocean can slowly evaporate and be replenished with new sources of water. When water evaporates, the mineral is left behind. Evidence of gypsum dunes has been found on the planet Mars as well.
What is the Chemical Formula for Gypsum?
The main components of gypsum are calcium sulfate (CaSO4) and water (H2O). Its chemical name is Calcium Sulphate Dihydrate and the chemical formula of gypsum is represented as CaSO4.2H2O. Gypsum and Anhydrite (CaSO4) are very similar chemically just that gypsum has 2 water molecules and Anhydrite does not contain any water molecules.
Physical and Chemical Properties of Gypsum Mineral
Gypsum was known as Spear Stone in old English since it takes a crystal-like form, projecting out of a rock like a spear. You can mix gypsum with water to get its original rock-like shape, and it can be hardened. Its recycling loop can be termed as a “closed recycling loop” since you can recycle it for a number of times and it never loses its quality. It is moderately soluble in water, and its solubility reduces with the rise in temperature, contrary to the behaviour of other salts. Here are some of its important chemical and physical properties at a glance:
Different Kinds of Gypsum
Since gypsum is found all over the world, its shape and texture also vary depending on which part of the world it is found. It is found in approximately 85 countries, and the biggest amount of gypsum is produced in North America. Gypsum has found its use in diverse fields, based on which it can be classified in the below categories:
Its different forms are:
Rock in dull colour
Alabaster which is its fine-grained variety
Gypcrete or gypcrust, which is a hard layer formed on the soil
Selenite Satin Spar has a fibrous texture with a silky lustre.
Types of gypsum products:
Type I – Impression Plaster
Type II – Dental plaster used in model material
Type III – Dental stone used in mounting material
Type IV – Die stone or high storage stone
Type V – High strength which is used when a high expansion is needed as die material like in fabricating base metal alloy castings
How is Gypsum Processed
Gypsum rock is first mined or quarried, then crushed and ground to a fine powder. It then goes through a process called calcining where heat at 350 degrees is supplied to the gypsum powder which removes 3/4th of the water molecules. Hemihydrate is the name of calcined gypsum which is then used in gypsum board, gypsum plaster, and other products. Its selection and preparation (like cleaning) determine the quality of plaster produced. The chemical reaction of this process can be given as:
(CaSO4, 2 H2O) + heat = (CaSO4, ? H2O) + 1.5 H2O
Uses of Gypsums – Some of the Important Uses of Gypsums include
Gypsum is in use for so many years, because there are so many uses of the Gypsum, a few of which are given below:
Constructing buildings
In making pottery and moulds
In dental appliances to make casts and moulds and impression material
Manufacturing plaster of Paris
Conditioning soil
Hardening material in cement
Filler ingredient in many foods
Gypsum is used in the manufacturing of cement, wallboard, soil conditioning, as a hardening Retarder in Portland cement.
Alabaster and Satin spar is the type of gypsum used for ornamental purposes.
In Agriculture, Gypsum is used as a fertilizer, it is also used as a fluxing agent, and in paper and textile, it is used as a filler.
Gypsum is heavily used as a building material, and in plaster of paris, as a matter of fact, about three-fourths of the total production is used for such purpose.
FAQs on Gypsum: Formula, Properties & Uses
1. What is gypsum and what is its chemical formula?
Gypsum is a naturally occurring soft sulfate mineral. Chemically, it is known as calcium sulfate dihydrate. The chemical formula for gypsum is CaSO₄·2H₂O, which indicates that each molecule of calcium sulfate is associated with two molecules of water, known as the water of crystallisation.
2. What are the main physical and chemical properties of gypsum?
Gypsum has several distinct properties that are important for its various applications.
- Physical Properties: It is a very soft mineral with a hardness of 2 on the Mohs scale. It is typically white or colourless but can appear grey, brown, or yellow due to impurities. It is also slightly soluble in water.
- Chemical Properties: When heated to about 120-150°C (393-423 K), it loses a part of its water of crystallisation to form calcium sulfate hemihydrate (CaSO₄·½H₂O), a substance commonly known as Plaster of Paris.
3. What are the most common uses of gypsum in daily life and industries?
Gypsum is a versatile material with many important applications. Some examples of its use include:
- Construction: It is the main raw material for manufacturing plaster, drywall, and plasterboard.
- Cement: An important example is its use as a retarder in Portland cement to control the setting time.
- Agriculture: It is applied to soil as a fertilizer and a conditioner for alkaline soils.
- Art and Ornaments: Certain varieties like Alabaster are carved for ornamental purposes.
- Food Industry: It serves as a food additive to improve texture and as a coagulant in products like tofu.
4. Where is gypsum naturally found?
Gypsum is a common evaporite mineral found worldwide in extensive sedimentary rock formations. It typically occurs in thick beds or layers formed by the evaporation of ancient saline water bodies. In India, for example, significant deposits are located in Rajasthan, Tamil Nadu, and Gujarat.
5. Is gypsum considered a harmful or toxic substance?
No, gypsum (calcium sulfate dihydrate) is generally considered non-toxic and safe to handle. It is not harmful if ingested in small amounts, although inhaling its fine dust can cause minor, temporary irritation to the eyes or respiratory system. It poses no long-term health risks.
6. How is Plaster of Paris chemically produced from gypsum? Explain with an equation.
Plaster of Paris is produced by heating gypsum in a process called calcination. When gypsum is carefully heated to a temperature of approximately 120-150°C (393-423 K), it loses three-quarters of its water of crystallisation and transforms into calcium sulfate hemihydrate (Plaster of Paris).
The chemical equation for this reaction is:
CaSO₄·2H₂O (Gypsum) + Heat → CaSO₄·½H₂O (Plaster of Paris) + 1½H₂O (Water)
7. Why is gypsum added to cement during its manufacturing?
Gypsum plays a crucial role as a retarder in the manufacturing of Portland cement. Without gypsum, the cement mixture would set almost immediately after water is added, a phenomenon known as a "flash set." This would make it impossible to transport, mix, and apply the concrete. The importance of adding 2-3% gypsum is to delay the initial setting time, allowing for proper handling and finishing.
8. What is the key difference between gypsum and Plaster of Paris?
The key difference between gypsum and Plaster of Paris is their chemical composition, specifically the amount of water of crystallisation attached to the calcium sulfate molecule.
- Gypsum is calcium sulfate dihydrate, with the formula CaSO₄·2H₂O.
- Plaster of Paris is calcium sulfate hemihydrate, with the formula CaSO₄·½H₂O.
9. Why is gypsum important for agriculture as a soil conditioner?
Gypsum's importance in agriculture comes from its ability to improve soil structure and provide essential nutrients. It is particularly effective for conditioning alkaline and saline soils. The calcium in gypsum displaces excess sodium from the soil particles, which helps improve water infiltration, drainage, and aeration. Furthermore, it serves as an excellent source of two key plant nutrients: calcium and sulfur, promoting healthier crop growth.
10. Are there any synthetic alternatives to naturally mined gypsum?
Yes, a significant synthetic alternative is Flue-Gas Desulfurization (FGD) gypsum. This is a by-product of coal-fired power plants that use limestone to scrub sulfur dioxide from their exhaust gases. The resulting FGD gypsum is chemically almost identical to natural gypsum (CaSO₄·2H₂O) and is widely used in manufacturing drywall and cement, offering a sustainable alternative that reduces the need for mining.
