Gypsum
2 of the 6 encyclopedias on this shelf carry an entry for Gypsum. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
jip'sum, a mineral composed of lime, sulphur, and water. Like marl, it is used as a fertilizer. Gardeners buy it in sacks under the name of land plaster. It is used also in the manufacture of glass and porcelain. When heated to drive off moisture gypsum falls into a powder which has the quality of hardening or setting quickly if moistened again. The most noted gypsum quarries in the world are near Paris, whence the name, plaster of Paris. Plaster of Paris ground fine is much used in the arts. Paperhangers mend walls with it. Plasterers use it in the finer sorts of work. Mixed with glue it is used for stucco work in the execution of cornices, flowers, garlands, festoons, fruits, scrolls, and other ornamental designs. Extensive beds are worked in various countries of Europe, especially England and France. In America, Nova Scotia , Michigan, Kansas, and Iowa produce considerable quantities. Gypsum is produced also in New York , Virginia, South Dakota , California, Utah, and Wyoming. We make half a million dollars' worth of plaster of Paris a year and import half as much more. Gardeners and farmers buy about $50,000 worth of raw gypsum a year for fertilizers. See Cardiff Giant
Collier's New Encyclopedia (1921)
calcium sulphate crystal. lized with two molecules of water Ca- So4 2H2O. It is often found by the decomposition of pyrites when lime is present. Gypsum calcined is called plaster of Paris, and is used for taking casts of statues. Gypsum is used as a manure; it facilitates the decomposition of rocks containing alkaline silicates. Technically gypsum is regarded as a mineral deposit, in some places constituting rock masses. It may be of any age. Near Paris it is Middle Eocene. Frapoli says that some gypsums were originally carbonates instead of sulphates of lime, and that they underwent metamorphism by the action of volcanic sulphurous or sulphurohydrous vapors. The production of gypsum in the United States in 1919 was about 3,430,000 short tons, valued at about $16,000,000.
What Has Changed in the Last Century
Both accounts treat gypsum mainly as a fertilizer and a plasterer's material, and Collier's put United States output in 1919 at about 3,430,000 short tons worth $16,000,000. The overwhelming use today is one neither entry mentions: gypsum wallboard, or drywall, which replaced wet plaster in most building after the Second World War and now consumes the great bulk of production; American output of mined gypsum runs to more than 20 million tons a year, supplemented by synthetic gypsum recovered from the flue-gas scrubbers of coal-fired power stations. Two later notes would have delighted these writers: the giant selenite beams of the Naica mine in Mexico, some over ten metres long, revealed in 2000, and the veins of gypsum found on Mars by NASA's Opportunity rover in 2011, taken as evidence that water once flowed there. Aiton's chemistry and Collier's formula, CaSO4ยท2H2O, remain exactly right.
Written for this edition, 2026.