Gypsum
Gypsum is an evaporite mineral most commonly found in layered sedimentary deposits in association with halite, anhydrite, sulfur, calcite, and dolomite. Gypsum (CaSO4.2 H2O) is similar to Anhydrite (CaSO4).
The chemical difference is that gypsum includes two waters and anhydrite is without water.
Gypsum is the most common sulfate mineral.
Occurrence of Gypsum
Gypsum is present in a variety of types and is of great economic value. It is colorless or white but can be tinted light brown, gray, yellow, green, or orange due to the presence of impurities. Single, well-developed crystals can be blocky with a slanted parallelogram outline, tabular, or blade. Twinned crystals are common and regularly form characteristic “fishtail”.
Many transparent, swordlike selenite gypsum crystals 61 ⁄ 2 ft (2 m) or longer can be found at the Cavern of Swords, Chihuahua, Mexico, one of the world’s most spectacular mineral deposits. Gypsum occurs in substantial beds formed by the evaporation of ocean saltwater. It likewise occurs as a modification item of sulfides in ore deposits and as volcanic deposits.
Properties of Gypsum
| Color | Colorless to white; might be yellow, tan, blue, pink, brown, reddish-brown, or gray due to impurities.
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| Luster | Vitreous, Sub-Vitreous, Silky, Pearly, Dull.
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| Crystal System | Monoclinic
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| Transparency | Transparent, Translucent, Opaque
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| Hardness | 2 on Mohs scale
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| Density | 2.312 – 2.322 g/cm3 (Measured) 2.308 g/cm3 (Calculated).
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Uses of Gypsum
Gypsum uses include the manufacture of wallboard, cement, plaster of Paris, soil conditioning, and a solidifying retarder in Portland cement. Varieties of gypsum called “satin spar” and “alabaster” are utilized for a variety of ornamental functions; however, their low hardness limits their sturdiness.
(a) Role of Gypsum in Agriculture
Gypsum, a hydrated calcium sulfate, is a mineral that occurs in large deposits throughout the world. Gypsum is applied to the soil as a source of calcium and sulfur. The calcium supplied by plaster in fertilizers is of value in crop production in areas where soils go through extensive seeping.
Sulfur has been recognized as a vital constituent of plants. For centuries, sulfur substances have been applied to soils because of their observed helpful impact on plant development. Aside from functioning as a constituent of protein and numerous other substances in plants, sulfur has an impact on chlorophyll development in plant leaves.
Although not a constituent of chlorophyll plants deficient in sulfur exhibit a pale green color. The root system of numerous plants has been observed to be significantly bigger by the application of sulfur. It has been reported that excellent crops are produced by the application of sulfur consisting of products such as gypsum.
(b) Role of Gypsum in Industries
When gypsum is heated under thoroughly regulated conditions, it loses 3 quarters of the water of formation. The resulting product is called Plaster of Paris. Plaster must not be heated up too strongly as the anhydrous salt is then formed which takes in water gradually. Such plaster is called ‘Dead burnt.
Plaster of Paris when mixed with half of its weight of water, forms a plastic-type thick mass and then sets to a hard permeable mass. This process is finished within 10 to 15 minutes. Throughout the procedure expansion of about 1% in volume also occurs, which fills the molds entirely, and thus a sharp impression is attained. Plaster of Paris is used for making plaster walls, casts of statuary, coins, and so on. It is utilized in surgical treatment; Plaster of Paris bandages are used for holding in location fractured bones after they have been set.
Special plasters contain plaster of Paris and other ingredients which differ with the demands of the use to which they are to be put. Two varieties of plasters are made.
(1) Cement Plaster
It is plaster of Paris to which generally glue or other oils have been included as retarders to prolong the time of setting.
(2) Hard Finish Plasters
These are made by the calcination of the anhydrous sulfate with alum or borax. These plasters are set very slowly however offer a difficult finish. When mixed with wood pulp and enabled to embed in the form of boards, it forms a material, much used in the construction of buildings as wallboards and partitions. Plaster is likewise utilized as a filler in paper markets.
Portland cement is made by highly heating a finely powdered mix of clay and limestone. The final product, known as clinker, is cooled and after that ground into a very fine powder. During the grinding, there is added about 2% of gypsum which prevents the cement from solidifying too rapidly. The addition of gypsum increases the setting time of cement.
MCQs about Gypsum
- What is the chemical composition of gypsum?
- A) CaSO4
- B) CaSO4.2H2O
- C) CaSO3
- D) CaCO3
- Answer: B) CaSO4.2H2O
- What is the primary difference in chemical composition between gypsum and anhydrite?
- A) Presence of water
- B) Presence of sulfur
- C) Presence of carbon
- D) Presence of nitrogen
- Answer: A) Presence of water
- In what type of deposits is gypsum most commonly found?
- A) Igneous
- B) Metamorphic
- C) Sedimentary
- D) Volcanic
- Answer: C) Sedimentary
- What impurities can cause coloration in gypsum crystals?
- What is the crystal system of gypsum?
- A) Cubic
- B) Monoclinic
- C) Trigonal
- D) Orthorhombic
- Answer: B) Monoclinic
- Which type of gypsum crystals are found at the Cavern of Swords, Chihuahua, Mexico?
- A) Blocky crystals
- B) Tabular crystals
- C) Twinned crystals
- D) Blade crystals
- Answer: C) Twinned crystals
- What is the hardness of gypsum on the Mohs scale?
- A) 4
- B) 6
- C) 2
- D) 8
- Answer: C) 2
- Which luster is not associated with gypsum?
- A) Vitreous
- B) Pearly
- C) Metallic
- D) Sub-Vitreous
- Answer: C) Metallic
- What is the primary use of gypsum in agriculture?
- A) Soil conditioning
- B) Plaster of Paris production
- C) Cement manufacturing
- D) Wallboard production
- Answer: A) Soil conditioning
- What is the role of sulfur in plant development with respect to gypsum?
- A) It enhances chlorophyll development.
- B) It inhibits root growth.
- C) It reduces calcium absorption.
- D) It has no impact on plants.
- Answer: A) It enhances chlorophyll development.
- What product is obtained by heating gypsum under controlled conditions?
- A) Satin spar
- B) Anhydrite
- C) Plaster of Paris
- D) Alabaster
- Answer: C) Plaster of Paris
- What is the primary use of Plaster of Paris in the medical field?
- A) Wallboard production
- B) Casts for statuary
- C) Cement manufacturing
- D) Soil conditioning
- Answer: B) Casts for statuary
- Which type of plaster is used in the construction of buildings as wallboards and partitions?
- A) Cement Plaster
- B) Hard Finish Plasters
- C) Satin spar plaster
- D) Alabaster plaster
- Answer: B) Hard Finish Plasters
- What is added to Portland cement during grinding to prevent it from solidifying too rapidly?
- A) Alum
- B) Borax
- C) Gypsum
- D) Plaster of Paris
- Answer: C) Gypsum
- What is the purpose of adding gypsum to Portland cement?
- A) To enhance color
- B) To increase hardness
- C) To decrease setting time
- D) To reduce density
- Answer: C) To decrease setting time
- What type of crystals are formed by gypsum during the modification of sulfides in ore deposits?
- A) Blocky crystals
- B) Tabular crystals
- C) Blade crystals
- D) Twinned crystals
- Answer: D) Twinned crystals
- Which term describes the expansion that occurs during the setting of Plaster of Paris?
- A) Contraction
- B) Compression
- C) Expansion
- D) Erosion
- Answer: C) Expansion
- What is the primary role of gypsum in the production of Portland cement?
- A) Increase setting time
- B) Enhance color
- C) Reduce hardness
- D) Promote rapid solidification
- Answer: A) Increase setting time
- What is the primary characteristic of “satin spar” and “alabaster” gypsum varieties?
- A) High hardness
- B) Low density
- C) Ornamental use
- D) Transparent crystals
- Answer: C) Ornamental use
- What happens when plaster is heated too strongly during the production of Plaster of Paris?
- A) It forms anhydrous salt.
- B) It becomes transparent.
- C) It gains water content.
- D) It loses its plasticity.
- Answer: A) It forms anhydrous salt.
- What is the primary function of gypsum in retarding the setting of Plaster of Paris?
- A) Increase setting time
- B) Decrease setting time
- C) Enhance hardness
- D) Promote transparency
- Answer: B) Decrease setting time
- Which property of gypsum makes it valuable for use as a solidifying retarder in Portland cement?
- A) Transparency
- B) Low density
- C) High hardness
- D) Unique expansion during setting
- Answer: D) Unique expansion during setting
Frequently Asked Questions (FAQs) – Gypsum: Occurrence, Properties, & Uses
General Questions:
- What is gypsum, and where is it commonly found?
- Gypsum is an evaporite mineral commonly found in layered sedimentary deposits, often associated with halite, anhydrite, sulfur, calcite, and dolomite.
- How does gypsum differ from anhydrite chemically?
- Gypsum (CaSO4.2H2O) contains two waters, while anhydrite (CaSO4) is without water.
Occurrence of Gypsum:
- In what types of deposits does gypsum occur?
- Gypsum occurs in layered sedimentary deposits formed by the evaporation of ocean saltwater. It is also found as a modification product of sulfides in ore deposits and volcanic deposits.
- What impurities can give color to gypsum?
- Gypsum can be colorless or white but may be tinted light brown, gray, yellow, green, or orange due to impurities such as iron, copper, and zinc.
- Where can one find large gypsum crystals, such as swordlike selenite gypsum crystals?
- Large selenite gypsum crystals can be found at the Cavern of Swords, Chihuahua, Mexico.
Properties of Gypsum:
- What is the crystal system of gypsum?
- Gypsum belongs to the monoclinic crystal system.
- Describe the transparency of gypsum.
- Gypsum can be transparent, translucent, or opaque.
- What is the hardness of gypsum on the Mohs scale?
- Gypsum has a hardness of 2 on the Mohs scale.
- What is the density range of gypsum?
- The measured density of gypsum is in the range of 2.312 – 2.322 g/cm3.
Uses of Gypsum:
- Name some common uses of gypsum.
- Gypsum is used in the manufacture of wallboard, cement, plaster of Paris, and soil conditioning. It also serves as a solidifying retarder in Portland cement.
- What are the limitations of using “satin spar” and “alabaster” varieties of gypsum?
- Despite being used for ornamental purposes, their low hardness limits their durability.
Role of Gypsum in Agriculture:
- How is gypsum applied in agriculture, and what benefits does it provide to the soil?
- Gypsum is applied to the soil as a source of calcium and sulfur. It helps in crop production, especially in areas where soils undergo extensive leaching.
- What role does sulfur play in plant development with the application of gypsum?
- Sulfur, a vital constituent of plants, enhances chlorophyll development, impacts protein synthesis, and contributes to the growth of the root system.
Role of Gypsum in Industries:
- What is the product obtained by heating gypsum under controlled conditions, and how is it used?
- Heating gypsum results in Plaster of Paris, which is used for making plaster walls, casts of statuary, coins, and more.
- How does gypsum prevent the rapid solidification of Portland cement?
- Gypsum, when added during the grinding of Portland cement, prevents it from solidifying too rapidly, thereby increasing the setting time.
Special Plasters and Portland Cement:
- What are the two varieties of plasters made for different uses?
- (1) Cement Plaster and (2) Hard Finish Plasters.
- How is Portland cement made, and what is the role of gypsum in the process?
- Portland cement is made by heating a mix of clay and limestone. Gypsum, added during grinding, prevents rapid solidification and increases the setting time.
Summary
The tutorial on Gypsum provides comprehensive insights into the occurrence, properties, and diverse uses of this evaporite mineral. Gypsum, commonly found in layered sedimentary deposits, holds economic value and exhibits various colors due to impurities. Its unique crystal forms, including twinned crystals and swordlike selenite gypsum, make it a fascinating mineral.
The properties of gypsum, such as its color, luster, crystal system, transparency, hardness, and density, contribute to its applications. Gypsum finds widespread use in manufacturing wallboard, cement, plaster of Paris, and as a soil conditioner. However, certain varieties like “satin spar” and “alabaster” are limited by their low hardness despite ornamental purposes.
The tutorial delves into the role of gypsum in agriculture, where it serves as a source of calcium and sulfur, enhancing crop production. The application of sulfur-containing products, including gypsum, has been reported to yield excellent crops.
In industries, gypsum undergoes controlled heating to produce Plaster of Paris, used for diverse purposes like making plaster walls and casts. Special plasters, including Cement Plaster and Hard Finish Plasters, cater to specific demands, while gypsum plays a crucial role in Portland cement production by preventing rapid solidification.
The tutorial concludes by emphasizing the varied applications and importance of gypsum in agriculture and industries, highlighting its role in enhancing soil fertility, crop production, and the production of construction materials.