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.
