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log this earthcache, send me an email with the answer
to the following questions:
1.
In what type of rocks does Silex form?
Indicates the name of a rock in which flint can be
found
2. How is Silex formed? What is
the process of formation of Silex called? What
minerals form the Silex mainly?
3. In several rocks of the wall,
in the rear area, mainly below, I could find flint.
Tell me its color, whether it is vitreous or not,
transparent or opaque, smooth or rough in texture.
4. Add a photograph of you in the
premises, or another in which you can see an object,
or your nick on a piece of paper
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Location
The Castle of Arévalo stands at one end of the town
on the edge of a plateau area, on the confluence of the Arevalillo
and Adaja rivers. The castle has an irregular pentagonal floor
plan, topped at each corner with small circular towers, except in
the case of the keep, which was built on top of a previous
Mudejar-style tower. Its structure, in which Italian influence can
be seen, is only a part of the original, as can be seen in the
engraving by Francisco Javier Parcerisa. It is made up of two
juxtaposed enclosures: one rectangular and the other triangular.
The corners are defended by circular towers, the keep of colossal
proportions and a fifth cube not preserved, masked by a
restoration that arbitrarily introduced architectural elements.
The lower part of the walls is made of ashlar masonry, a material
probably from a previous castle, and the upper part is made of
brick, a characteristic element of the region. The keep, with a
sloping semicircular floor plan, is entirely made of ashlar
masonry, although it currently shows brick finials as a result of
the aforementioned restoration, which made the curvilinear parapet
with loopholes, built in the 16th century when adapting the castle
to a prosion, disappear.
Along its upper part there are sentry boxes and blind
machicolations similar to those of the Castillo de Coca, which
suggests that they are works by the same anonymous architect.
Its location is disfigured, since on the part that faces the town,
the weakest due to its accessibility, there should have been a
moat, an essential complement for its gun emplacements at ground
level. The War of the Spanish Succession and the War of
Independence gradually ruined it, disassociating itself from royal
property in the Courts of Cádiz (1812), and its enclosure was used
as a cemetery.
Flint
Flint, also traditionally
called flint, is a heterogeneous material, that is, it is not
properly a mineral but a rock. It is made up of a mixture of
siliceous minerals, such as quartz in microcrystalline form,
quartz in fibrous cryptocrystalline form (chalcedony), moganite
and opal, in proportions that depend on the deposit or even the
specific point from which it has been extracted within the same
deposit. Along with the siliceous minerals, the minerals that form
the encaxant also appear, such as calcite, anhydrite, dolomite and
clay minerals, especially sepiolite. It may also contain traces of
fossils. Flint is formed by replacement (diagenesis) of
pre-existing sedimentary rocks, forming nodules or bands.
Source
The exact mode of flint formation is still unclear, but it is
believed to occur as a result of chemical changes in compressed
sedimentary rock formations during the diagenesis process. One
hypothesis is that a gelatinous material fills cavities in the
sediment, such as holes drilled by crustaceans or mollusks, and
that the sediment becomes silicified. This hypothesis undoubtedly
explains the complex shapes of the flint nodules found. The source
of dissolved silica in the porous medium could be the spicules of
siliceous sponges (demosponges). Certain types of flint, such as
that from the south coast of England and its counterpart on the
French side of the Channel, contain trapped fossilized marine
flora. Pieces of coral and vegetation have been found preserved
inside the flint, similar to the insects and plant parts inside
the amber. Fine cuts of the stone often reveal this effect.
Flint sometimes occurs in large flint fields in Jurassic or
Cretaceous deposits, for example, in Europe
Properties
It is a hard and very resistant material, as corresponds to what
is usually its main component, quartz, 7 on the Mohs scale. It has
a conchoidal fracture, forming cutting edges, and a grain size
that depends on the deposit. The color is very variable, from
white to black, brown colors being especially frequent, with a
banding of different color tones. The black flint with a very fine
grain is called lydite, and was used as a touchstone to assess the
purity of precious metals.
Applications
Due to its hardness, it was used in the Stone Age to make cutting
tools, due to its ability to break into flakes (conchoidal
fracture, straight blades with slight curves) with very sharp
edges. Initially, occasional collection was used, but soon some
deposits were exploited in an organized way. The oldest known
workings are located at Nazlet Safaha, Nazlet Kather and Beit
Allam, on the terraces of the left bank of the Nile, in the area
of Sohag, Egypt.
Since flint produces sparks when struck with other hard rocks or
metals, it was also used to start fires. Later it was used in the
first firearms, spark weapons, to initiate the combustion of
gunpowder. This application continues to this day in lighters,
although the flint has been replaced by ferrocerium bars, a
material that is also called flint due to its similar use.
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