Ubiquitous in many classroom since the 19th century , glass and chalkboards are familiar to most of us . white-hot , powdery and prone to sticking to those surfaces where it is put ( and just as soft to pass over aside ) , chalk and its come with control board are excellent instructional assistance . Notably , however , most chalk today is n’t technically chalk at all , but gypsum .
Chalk and gypsum have both been mine since ancient times . ice ( calcium carbonate ) has been found in cave paintings that date back to 40,000 BC , while gypsum ( calcium sulphate ) has been used as a mortar for construction since the dawn of civilization , and is even find in the Egyptian pyramids .
Similar and yet distinct , chalk is a base ( an alkali that negate acids ) that is composed of calcium and oxygen unite with carbon ( CaCO3 ) , while gypsum is a salt ( the product of a base and dose reacting and both becoming neutralized ) , made up of atomic number 20 and atomic number 8 combined with sulphur .
Both are believed to be formed in similar way . methamphetamine is a limestone down payment created as plankton ( tiny marine being ) boil down Ca in their bodies while living , then strip the calcium out after they die and conciliate onto sea level ; over millennia , with child deposits are formed , and as the seas retreat , chalks depositsremain .
Gypsum ’s origins are similar , but in improver to being be of the atomic number 20 create by the death of millions of plankton , gypsum also hold some of the salt that was left behind as the ocean evaporated .
Traditionally chalk has been used for drawing and writing , and by the final stage of the 18th century , with progress in slate quarrying ( slate was originally used for write tablets and chalkboard ) , write slate cover with chicken feed letter of the alphabet , symbols , number and figures were commonplace . Gypsum on the other hand , had been used primarily in construction , such as for the said trench mortar , as well as in the manufacturing of window .
Nonetheless , both are susceptible to a summons that develop stick of themselves that , when conjure against sure service , leave washable mark .
After quarry , each is crushed , earth , launder and sieve . With gypsum , it must also be dehydrated in a outgrowth that involve gamey temperature to concentrate its body of water content from nearly 21 % to about 5 - 6 % ; to make classroom chalk , the fabric is mixed , again , with water ( and colored pigment , if desired ) , and to produce more alien pastels , such as used for nontextual matter drawing , pigment as well as cadaver or oils are also added . For the former , the glass is baked , while with the latter , it is aura - dried .
It ’s not readable why gypsum has replaced chalk for writing on blackboard ( which today are mostly green , but that ’s another tarradiddle ) . While historically crank has been remarkably dusty , mod manufacturing method , including broil the chalk and coat it with products like shellac , have reduce the job for both fabric .
The most likely reason is that gypsum is abundant , well mined and processed in enormous quantities . The mineral is mine in more than 90 countries , include Canada , Mexico , Spain and the United States . In the U.S. , 19 states ( notably California , Iowa , Nevada , Oklahoma and Texas ) have aerofoil - mining operations , and the U.S. alone produces more than 30 million tons of the stuff each class .
Sometimes called “ the tilt nobody make out , ” gypsum can well be turn into a okay powder ( by desiccate it ) , while it also has the noteworthy quality of being “ the only born substance that can be restored to its original rock - comparable state of matter by the addition of water alone . ”
Since it can be reconstituted , it can be fashion into any of a myriad of shapes and modify for various uses . Common software let in plaster of Paris , creating mud molds from which a variety of credit card products are formed ( such as plastic cup and plate ) , the manufacture of glass , as an constituent in cement and in wallboard ( this last has been a boon to humanity as gypsum is naturally terminate resistant ) .
Non - toxic , gypsum also pops up in plant food and territory conditioners , hair products , to make plaster of tooth , to turn mushroom , brew beer and bind tofu ( which also has the added benefit of making bean curd an splendid atomic number 20 source ) .
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Bonus Fact :
In 2013 , North American gypsum manufacturers report sales of gypsum board , alone , of more than $ 3 billion , annually ; together they produced more than 20.5 billion square understructure of dry wall , which is found in more than 97 % of American buildings .
Melissa writes for the wildly popular interesting fact websiteTodayIFoundOut.com . To take to Today I Found Out ’s “ Daily Knowledge ” newssheet , flick hereor like them on Facebookhere .
This posthas been republished with permission fromTodayIFoundOut.com . Image byDanielChloe Blanchfieldunder Creative Commons license .
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