Slate
Slate is a fine-grained,
homogeneous,
metamorphic rock derived from an original
shale-type
sedimentary rock composed of
clay or
volcanic ash through low grade regional
metamorphism. The result is a
foliated rock in which the foliation may not correspond to the original sedimentary layering.
Slate is mainly composed of
quartz and
muscovite or
illite, often along with
biotite,
chlorite,
hematite, and
pyrite along with, less frequently,
apatite,
graphite,
kaolin,
magnetite,
tourmaline, or
zircon.
Slate can be made into
roofing slates (sometimes called
roofing shingles in the
United States), because it has two lines of breakability: cleavage and grain. This makes it possible to split slate into thin sheets. Fine slate can also be used as a
whetstone to hone knives. Because of its thermal stability and chemical inertness, slate has been used for laboratory bench tops and for
billiard table tops. In 18th and 19th century schools, slate was extensively used for
blackboards and individual
writing slates for which slate pencils were used.
Slate-producing regions include
Cornwall (famously the town of
Delabole) and
Wales in the
United Kingdom (see
Penrhyn Quarry),
Portugal, the east coast of
Newfoundland, the Slate Belt of Eastern
Pennsylvania, and the Slate Valley of
Vermont and
New York.
Granville, New York, of the Slate Valley claims to be the colored slate capital of the world.
Slate is also found in the
Arctic and was used by the
Inuit to make the blades for
ulus.
Traditional
Go equipment uses slate for the black pieces.
*
List of rocks*
Skiddaw Slate*
Tile*
Welsh Slate Museum*
History of the Welsh slate industry*
Slatesite — bilingual site focusing on Welsh slate
*
John T F Turner - A Familiar Description of the Old Delabole Slate Quarries, 1865
