Calcium Carbonate

Figure 1. White and colored chalk
Source: Closeup on chalk color. http://www.publicdomainpictures.net
/view-image.php?image=124540&picture=chalk-color (accessed Oct 25, 2016)  

Aragonite sounds like some mythical dragon but in fact it is just another name for calcium carbonate, or chalk.¹ Yes, the solid, cylindrical, white or colored² object your teacher uses to write on the chalkboard while you're daydreaming or half-asleep. You may or may not know this but it is actually very abundant on Earth, so we are able to mine it from chalk, limestone, or marble reserves.¹ After it is mined, coloring pigments can be added to it to make it any color you could ever want.³ After the coloring pigments are added, manufacturers make the mixture into a clay-like consistency using water then it is baked in a giant oven.³ It can also be made in a laboratory by reacting calcium chloride and sodium carbonate together, if you do try this you will find a white to tan colored solid substances in your solution, the solid is calcium carbonate.¹

Do you care about the health of your teacher? If not, move on to the next paragraph. Your teacher is exposed to chalk through chalk dust inhalation, skin contact, or sometimes even on accident by ingestion or eye contact.² Perhaps they ingested it to get their recommended daily calcium dose of 1000mg/day, but I don't recommend this as chalk isn't purely calcium carbonate.² Although if it was pure calcium carbonate, as long as they don't eat 6450 mg/kg of their body weight then they should survive.² Though your teacher will most likely show signs of skin and/or eye irritation, they may even cough or sneeze.² In more serious cases, if they ingest too much it may lead to blood and kidney disorders.² Now, to save your teacher from these side effects educate your teacher about available alternatives including chalk markers or completely switching to using a whiteboard and dry-erase markers.

There are many applications of the chemical, calcium carbonate, other than making chalk. It can also be used to make antacids,¹ which you take when you get heart burn or indigestion because one characteristic of calcium carbonate is that it is basic, and so it is able to neutralize acids, ² in this case stomach acid which is the cause of heart burn.¹

Have you ever looked at a stick of chalk and wanted to eat it? If so, get yourself to a mental hospital because you may have Pica Syndrome.⁴ It is a mental condition where regularly non-food substances are desired to be eaten, most common choice being sticks of chalk.⁴ Freaky.

References:

1. Schlager, E., Weisblatt, J., & Newton, D. Chemical Compounds [Online]; GALE: Detroit, 2016; p143-146. http://library.mtroyal.ca:2200/ps/i.do?p=GVRL&sw=w&u=mtroyalc&v=2.1&it=r&id=GALE%7CCX3441700040&asid=ae40f7ad2d4073bcb3d0a1d5f5442b0c (accessed Oct 25, 2016)
2. National Center for Biotechnology Information. Calcium Carbonate. https://pubchem.ncbi.nlm.nih.gov/compound/calcium_carbonate (accessed Oct 25, 2016) PubChem Compound Database CID=10112.
3. Chalk Background. http://www.madehow.com/Volume-1/Chalk.html (accessed Oct 25, 2016)

4. EnviroHealth Expert. Craving and eating white chalk. http://www.health24.com/Experts/Question/craving-and-eating-white-chalk-20070927 (accessed Oct 25, 2016)