Chalk
From Simple English Wikipedia, the free encyclopedia
Chalk is a sort of limestone. The air and the water do not wear chalk away easily, so when chalk is next to the sea, it often makes a big cliff. The "White Cliffs of Dover" in England are a good example of this. When chalk is near the top of the ground, it often makes chalk hills. Chalk holds water, so these chalk hills have a lot of water in them, and when the weather is very dry, water comes slowly from the chalk.
Blackboard chalk is not chalk. Really, it is gypsum (calcium sulfate), but often people say only "chalk" for it. We use it for drawing on hard things, because it is soft. If you rub the end of the chalk on something that is hard and rough, some of the chalk in the stick will come off and leave a mark. We usually write with chalk on a chalkboard or blackboard. You can use a chalk eraser or water to clean the chalk marks away so the board is blank again. Shops usually sell blackboard chalk in sticks which are about 5 cm long.
You can get big pieces of soft chalk for children to write on the ground with, for example on concrete (for example a sidewalk) or on asphalt (for example a driveway). It is usually okay to write on the ground with this kind of chalk, because the rain will wash the chalk away.
Tailors' chalk is also not chalk. Really, it is talc (magnesium silicate). Tailors use it to draw on material when they are making clothes.
People in the military say a chalk is when an aeroplane is carrying a special load, especially a group of soldiers in a single aeroplane. "U.S. Army Ranger Chalk Four" was the group which was first hurt in the Battle of Mogadishu in Somalia.