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In this series we will be looking at different types of rocks and rockformations.
For this Earthcache we will take a look at the three basic rocktypes and ways to identify them. Rocks fall in three major groups and they are as follow:
Igneous Rock - a rock that crystallized from molten rock or magma.
Sedimentary Rock - a rock that was deposited from a fluid; water, wind, or ice (yes, ice is a fluid.
Metamorphic Rock - a rock that was recrystallized in the solid.
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To identify in what group a rock falls in there is a couple of steps that you can follow. The first step is first and foremost a vissual one.
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Igneous Rocks commonly have a composition consisting of olivine, pyroxene, and feldspar crystals. They also may exhibit a ropy type of banding, this is caused by cooling lava.
The colours of these minerals are as follow.
Poroxene:Characteristically, pyroxenes are dark green to black in colour, but they can range from dark green to apple-green and from lilac to colourless, depending on the chemical composition.
Olivine:Yellow to yellow-green
Feldspar: pink, white, gray, brown.
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Sedimentary Rocks are generally layered and exhibit a clastic texture. They also preserve fossils and other organic remains. Common places that sedimentary rocks occur at are river beds, deltas, beaches, sand bars, and extensive flat layers.
Sedimentary rock can be from creamy coloured to greenish grey and black depending on what colour the sediments were that formed them.
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Metamorphic Rocks have textures such as folds, fractures, faults, and foliation. Foliation is the most common indicator of a metamorphic rock. Often the composition consists of garnet, tourmaline, and mica. It is a metamorphic rock if it contains serpentine, epidtoe, graphite, galena, or sphalerite because these minerals only occur in metamorphic rocks. The colour of these minerals are as follow:
Garnet:virtually all colors, blue very rare
Tourmaline:Most commonly black, but can range from colorless, brown, violet, yellow, orange, blue, red, green, pink, or bi-colored, or even tri-colored.
Mica:purple, rosy, silver, gray (lepidolite); dark green, brown, black (biotite); yellowish-brown, green white (phlogopite); colorless, transparent (muscovite)shiny and flaky.
Epidtoe:Pistachio-green, yellow-green, greenish black.
Graphite:Iron-black to steel-gray; deep blue in transmitted light.
Galena:Lead gray and silvery
sphalerite:Brown, yellow, red, green, black.
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In every one of the three types of rock there is a multitude of different kinds, depending on the ratio of the minerals that formed that specific rock. It takes years of experience to identify every single variation and a lot of the time rock specimens get analyzed in laboratories.
This should not discourage anyone to start identifying rocks. The more rock samples you study the more one gets accustamed to the names and charectiristics of each mineral that makes up each rock type.
Information was obtained from wikipedia.
On site questions.
#1 using the above information try and place the rock formation at GZ in one of the three types of rock groups with an explanation why you think so, please try and include as much information as possible.
Forward your answers to our Kingosric handle.
Please forward as soon as possible.
Additional Hints
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