Slate
Slate is
a fine-grained rock that can easily be split into thin, durable
sheets. It consists mainly of grains of mica and quartz, plus
smaller amounts of chlorite, hematite, and other minerals. Most
slate is grey to black in colour, but the rock may be red or
purple, depending on its mineral content.
Slate is a metamorphic rock. Most slate is formed below the
earth's surface by changes in the makeup and appearance of shale,
a sedimentary rock. Shale consists of clay and fine particles
of quartz. Heat from deep in the earth changes some of the clay
in shale into mica and chlorite. Slate results when pressure
created chiefly by mountain-forming movements in the earth's
crust squeezes the mica and other minerals into parallel layers.
The building industry uses slate for roofing and flagstone because
the rock is weatherproof and long lasting. Slate is also used
to trim the fronts and lobbies of buildings.
Slate 1 :
Slate is a split stone and is one of the world's oldest natural
products. Slate is available in various colours. Some shades
will change colour on exterior use; therefore a non-fading shade
should be specified for exterior applications. Water absorption
of slate in accordance with ASTM C121.
Slate 2 :
There are items on the market that can be written on again and
again. These are 'slates', I guess that word is right, that
consist of a layer of transparent film, under this film there
is a layer of magnetic dust or something but I don't know the
exact make up of the materials used. Then one has a pen to go
with that with which one can draw a line over the magnetic part
of the board which will be black. When one wishes to erase the
drawing/writing/sketch there is a little handle on the side
connected to an elongated magnet under the magnetic film. When
you move this handle from right to left then all the magnetic
particles get evened out and the screen is blank again. A year
ago I saw this on TV too, but this time as a tool to be used
in offices as a substitute for the 'flip over', this in order
to spare paper.
What you are describing sounds like the 'Etch a Sketch'. If
you have ever tried it, actually writing on it is very difficult.
There is a simple writing device which is a transparent gray
film over a slick, black cardboard background. You write or
draw on it with a blunt stylus. This causes the film to stick
to the background, making a line. When you want to reuse it,
you simply pull up one end of the sheet and it is 'erased'.
For temporary drawing or writing, it would be hard to beat the
simplicity of chalk and slate! Also available in multiple colors!
Paper is still important, as it would be the lowest-tech medium
which would have any chance of surviving for a long period of
time. Writing should not be allowed to die out!
Slate 3 :
Slate is basically metamorphosed shale. Shale is made up of
slit and clay that is similar in composition to sandstone except
that the particle size is much smaller. The shale is subject
to heat and pressure and the fine particles are "melted" together
to form slate.
Slates are a natural cleft material and are typically used for
flooring or roofing applications. Some slates are available
in large slabs and can be used for counter tops.
Most slates are suitable for exterior and interior applications.
Be careful when specifying green slates as their color may change
or fade with time.
