The Story of Slate - 1923 - Page 3
new minerals, the chief of which are mica and chlorite, both consisting of minute flakes and scales.
Millions of these tiny flakes overlap each other like shingles on a roof.
As they all lie in one plane there is developed a remarkable tendency for the rock to split with great ease in one direction.
This splitting tendency or cleavage is the most important property of slate.
Slabs 4 x 6 feet in size, or larger, may be readily split to less than ½ - inch thick, and there have been instances where sheets 8 x 16 inches have been split to the remarkable thinness of 1/64 -inch.
The little tabular or flake-like grains are cemented under intense pressure which gives slate unusual strength.
While human hands can take slate apart they can never put the grains together again with the same regularity, nor can they give it the same strength as is possessed by the natural rock.
The fineness of grain, uniformity and strength of slate fit it peculiarly well for many purposes.
Remember now that no rocks are everlasting and slate is no exception to this rule.
It is noteworthy, however, that slate consists of non-metallic minerals that are very enduring and that resist remarkably well the forces of the weather that are ever at work in wearing down the rocks.
Now what are some of the uses for which this remarkable product is best adapted?
Its enduring properties and its tendency to split into thin sheets led to its early use for making weatherproof roofing for houses, and this is still one of its important uses.
Black, gray, green, red, purple or mottled slates form many of the most beautiful roofs to be found in the world.
It has also been found that high-grade slate is an excellent nonconductor of electricity, and as it can be readily shaped, drilled and polished, it is widely used for electrical switchboards.