Question

3. A rock used for making slates and blackboards.​

Answer 1

Explanation:

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 Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.

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Answer 2

Answer:

slate

it is a metamorphic rock.

sedimentary rock called shale is converted into a slate after many years.