There are three main types of rocks. They are

There are three main types of rocks. They are sedimentary,
metamorphic, and igneous. What differs these rocks and can be used to identify
them has to do with the different ways they are formed.

Sedimentary rocks are rocks
that have been formed from particles of pebbles, shells and many other
fragments of material. These sediments then come together because of deposition.
They are deposited by movement within the environment. Sedimentary rocks can then be classified as clastic or
non-clastic. Clastic rocks
are rocks that have been formed by previously existing rock fragments that have
been cemented together. Clastic sedimentary rocks have variable grain sizes,
shapes and porous spaces. Non-clastic rocks
are formed through minerals being deposited. Non-clastic sedimentary rocks have
a crystalline texture, which is an interlocking arrangement of crystals. The shape of the
sediments is an important characteristic that classifies sedimentary
rocks. The roundness of them represents how the grains were transported and more
round grains show that they have travelled further. Sedimentary rock identification is primarily based on composition.
One factor that can also make these rocks easily
distinguishable is that you can often see sand, pebbles, or stones in the rock,
and it is usually the only type that contains fossils. Rock number six observed in the experiment represents
a sedimentary rock. Specifically, this rock is bio clastic limestone. I know this because it is composed of many skeletal
fossil fragments materials cemented together by a carbonate material. I
could tell this was true when I performed the “fizz” test and the rock
formed bubbles when a drop of HCl was added. Another
observable feature of this rock is that the particles are round, which shows this
rocks particle were formed in a high energy environment.

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Metamorphic rocks are composed of other rocks
that have come together and been subjected to high heat, high pressure or hot
mineral-rich fluids. When the rocks go through this process, it can result in ribbon
like layers and may have shiny crystals, which formed by minerals growing
slowly over time on their surface. Texture is a way that metamorphic rocks can
be identified. Their texture can be divided into two groups, foliated and
non-foliated. If it is
foliated, it shows a distinct layered character,
which is the minerals aligned with each other. Non-foliated is the exact
opposite of this and shows no patterns of layering. The different types of
foliation are then used to identify more specifically what the rock is. There
are four different types of foliation;
salty cleavage, phylitic foliation, schistose foliation, and gneissic banding. Salty
cleavage is composed of platy minerals that are in general too small to
see. Phylitic foliation is composed of platy minerals that are slightly larger but
are still too small to see with the naked eye. Schistose foliation is
composed of larger minerals that are visible. Gneissic banding is composed
of alternating layers of dark and light minerals. Rock number one is an example of a metamorphic rock.
We identified this rock as garnet schist. We know this because its
layers classify it as a metamorphic rock and its gray, silvery color indicates
it is a garnet schist.
            Igneous rocks are formed when magma cools
and hardens. The magma can either cool inside the earth or it can erupt onto
the surface from volcanos as lava. When lava cools very quickly, no crystals
form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped
in the rock during the cooling process, leaving tiny holes and spaces in the
rock. The composition of igneous
rocks can be identified by its chemical composition. The chemical composition
can be determined by the rocks color. Light colors indicate a felsic composition. This
means that they are rich in silica. Dark colors indicate a mafic or
ultra-mafic composition. This means that they are the opposite and that
they have very little in silica but that they have a lot in iron and
magnesium in its composition. This can be a tricky way to identify a rock
though because igneous rocks may have a felsic composition and because
mafic rocks may contain light colored minerals. Another classification of
igneous rocks is its texture. The texture is based on crystal size. Pegmatic texture is composed of very large crystals. Phaneritic
texture is composed of crystals that are
large enough to see but smaller than pegmatitic, and the entire rock is composed of crystals. Aphanitic
texture is a fine-grained texture where the
crystals are too small to see. Porphyritic texture is a mixture of crystals of two different sizes.
One example of an igneous rock we observed in lab
was rock number eight. We identified this rock as vesicular olivine
basalt. We can see it is vesicular because of the porous surface and it is
olivine because of the green crystals. We can tell this rock is basalt because
it is a gray to black volcanic rock that is fine
grained due to rapid cooling of lava on the Earth’s surface.

 

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