Put It On The Slate EarthCache
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Honister Slate mine is at the top of the Honister Pass in
Borrowdale in the Lake District. You can watch slate being riven
(or split) using processes that have changed little over the past
300 years.
Fully guided tours into the mine are available several times a day,
detailing the history and spectacular features of the mine. The
tour shows the current workings of the mine, and how a mixture of
modern and traditional methods, is still extracting the slate which
was formed some 400 million years before Tyrannosaurus Rex strode
the land. Honister slate is a distinctive green slate, though
Lakeland slate comes in a variety of shades and colours. It is a
strong and durable material, excellant for roofs , and also for
floors and walls. Slate was being exported through Piel Harbour in
1688, long before the opening of the Furness Railway in 1846. It
was taken by packhorse over the western edge of Great Gable and
Wasdale, for loading onto boats at Ravenglass. In the late 17th
Century, it was used by Sir Christopher Wren at the Royal Hospital,
Chelsea, and at Kensington Palace. Slate is a fine-grained, clayey
metamorphic rock that cleaves, or splits, readily into thin slabs
having great tensile strength and durability; some other rocks that
occur in thin beds are improperly called slate because they can be
used for roofing and similar purposes. True slates do not, as a
rule, split along the bedding plane but along planes of cleavage,
which may intersect the bedding plane at high angles. Slate was
formed under low-grade metamorphic conditions—i.e., under
relatively low temperature and pressure. The original material was
a fine clay, sometimes with sand or volcanic dust, usually in the
form of a sedimentary rock (e.g., a mudstone or shale). The parent
rock may be only partially altered so that some of the original
mineralogy and sedimentary bedding are preserved; the bedding of
the sediment as originally laid down may be indicated by
alternating bands, sometimes seen on the cleavage faces. Cleavage
is a super-induced structure, the result of pressure acting on the
rock at some time when it was deeply buried beneath the
Earth’s surface. On this account, slates occur chiefly among
older rocks, although some occur in regions in which comparatively
recent rocks have been folded and compressed as a result of
mountain-building movements. The direction of cleavage depends upon
the direction of the stresses applied during metamorphism.Slates
may be black, blue, purple, red, green, or gray. Dark slates
usually owe their colour to carbonaceous material or to finely
divided iron sulfide. Reddish and purple varieties owe their colour
to the presence of hematite (iron oxide). . The principal minerals
in slate are mica (in small, irregular scales), chlorite (in
flakes), and quartz (in lens-shaped grains). Slates are split from
quarried blocks about 7.5 cm (3 inches) thick. A chisel, placed in
position against the edge of the block, is lightly tapped with a
mallet; a crack appears in the direction of cleavage, and slight
leverage with the chisel serves to split the block into two pieces
with smooth and even surfaces. This is repeated until the original
block is converted into 16 or 18 pieces, which are afterward
trimmed to size either by hand or by means of machine-driven
rotating knives. Slate is sometimes marketed as dimension slate and
crushed slate (granules and flour). Dimension slate is used mainly
for electrical panels, laboratory tabletops, roofing and flooring,
and blackboards. Crushed slate is used on composition roofing, in
aggregates, and as a filler. Principal production in the United
States is from Pennsylvania and Vermont; northern Wales provides
most of the slate used in the British Isles. The co-ordinates take
you to the entrance of the slate mine. To log the cache, upload a
photo of you or your GPS with the slate entrance sign to the right
as you enter and answer the following questions 1) What gives
Honister slate its green colour. 2) What is the slate used for.
Thanks must also go to Grufftymilo who helped us to get the Earth
Cache up and running
Additional Hints
(No hints available.)