INDIAN GEOGRAPHY

Detailed explanation-1: -A blackboard (also known as a chalkboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known, when used for this purpose, as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.

Detailed explanation-2: -Blackboards are nothing about an evolution of wooden slate. The only literal difference between the two was position–vertical and horizontal–blackboard was kept vertical while slates were used horizontal.

Detailed explanation-3: -Because of their smoothness uniformity permanence and attractiveness slate blackboards are superior to all other types of blackboards now in use."

Detailed explanation-4: -Most modern chalkboards are made of porcelain enamel. In this particular manufacturing process, a tough and durable material such as steel is used as the base. There are several thicknesses of steel used in the manufacture of chalkboards, but the most common is 22-gauge.

Detailed explanation-5: -Gneiss is a dark grey shiny rock made by metamorphism of shale. Used to make slates and blackboards.