We all have used chalk to write on the blackboard during our school days. Properties of chalk are unique and hence, different from other kinds of rocks that can be used to write and erase. Chalk is usually of white color but is also available in different colors. Many of us used to eat chalk in our childhood. Oops!
1. How did it Form?
It is a form of limestone which is white to greyish in color. It started depositing in the extensive continental shelves almost 145 to 66 million years ago. It is believed that during that era, the climate was so arid that there was less erosion. Due to this, chalk started to deposit in the depths of the earth of hundreds of feet. The quality of chalk is considered pure because of the minimum amount of erosion around it. (See What Is a Geode?)
2. What is it Made of?
One of the properties of chalk is that it is a very pure lime mud that is only composed of plankton skeletons. The microscopic skeletons of the dead plankton i.e., microorganisms found in water bodies, have calcite as the constituent component in them. Thus, chalk is pure Calcite viz Calcium Carbonate and other minerals.
3. Why do they have White Color?
The chalk was formed when the sea levels were very high. As a result, the land and its sediments were not mixed with the undersea sediments. Since these sediments were not exposed to any impurities, they still have white color. (See What is the Peanut Gallery?)
4. Where is Chalk Found?
The large deposits of chalk that can be seen today have taken the shape of huge cliffs. This is because, over these millions of years, the water level gradually lowered down so much that the deposits formed in the sea bed now look like high cliffs. This is another one of unique properties of chalk.
- White Cliffs of Dover, Kent, England is an example of the deposits of calcite.
- There are also huge chalk caves situated in the Champagne region of France.
- While the highest chalk cliff was a huge island millions of years ago, it is now divided and located in Germany at the Jasmund National Park and in Denmark at the Mons Klint.
5. Who Invented Chalk Sticks?
Earlier, people converted rocks into sticks by grinding them and then, mixing them with water and clay. It was then made into odd shapes and dried so that it could be convenient to hold while drawing.
During the 19th century, the use of chalks on blackboards became popular. These chalk sticks are usually 10 mm thick and 80 mm long. Initially, the chalks were only of white color because the boards were black.
According to sources, colored chalks were invented by James Pillans in the year 1814, by mixing porridge, crushed white chalk, and dyes together. As years passed, colored chalk became popular since the kids enjoyed colorful drawings. However, the properties of the chalk remained the same even if they were colored. (Also see 5 Fun Kitchen Science Experiments for kids)
6. What is Blackboard Chalk made of?
These sticks which are used to write on the blackboards are made up of calcium carbonate, which is found in limestone sediments. The calcite contents in these chalk sticks range from 40% to 60% and have a component called calcium sulfate. It consists of calcium salt and hydrate (CaSO4 and 2H2O) and is derived from the gypsum stone. Hence, these are the properties of chalk. (See Why is Blackboard Green?)
7. Who was the First to Use Chalk?
During the pre-historic period, chalks were used to make cave drawings. Various pieces of evidence have been found in several caves by historians and archaeologists. The first person to use chalk on a blackboard is said to be George Baron. He used white chalk during one of his mathematics lectures on 21st September 1801.
8. What are the Uses of Chalk?
- It was and is still used to write and draw on surfaces. The larger bars are used to draw on pavements and sidewalks.
- It is also used in agriculture as it has the quality to raise pH levels of the soil.
- Putty that is used by builders also contains chalk.
Some kids consider eating it too, but it may not be a good choice to do so. There are many risks related to this habit.
9. What is Red Chalk?
Even though we have mostly seen white chalk and believe that it is the natural color of the chalk, but red chalk also occurs naturally. It is formed in the ground with layers that are 300 meters to 400 meters thick. And within these layers of red chalk, there are other sediments like flint and chert. The red color of this sediment is due to the iron oxide pigment present in these sediments.
Properties of chalk and its purity have remained the same throughout time. So, what is backboard chalk made of? In simple words, the components of chalk are calcite, water, and clay. Hence, it is advisable to not eat it.