What is Slate?

Million of years ago, fine-grained clay particles settled on the bottoms of lakes and inland seas and formed a soft mud. This later hardened into the mud-rock that is called "shale". During this period, the earth’s crust moved and shifted. The layers of shale, covered by beds of other rocks, were folded up into wrinkles. These were flattened and squeezed so hard that the shale became slate.

The clay particles making up the slate were deposited by the lakes and seas in layers. Even after the pressure changed the shale to slate, the many separate layers of the deposits remained. And today we can split slate into wide, thin plates because it did stay in layers.

The most common colors of slate are dark grey and black, thought it may also be red, green, or various shades of grey. The reason it is chiefly  black is that the living matter in the original mud left carbon material.


Slate occurs only where mountains-making pressure and earth changes have been active upon the layers of old shale. Slate is used for many purposes. One of its chief uses is as a roofing material for homes and buildings of all kinds. Among other things made from slate are blackboard, table tops, and draining boards.

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