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Common Rocks Lab # 3
1st part of Experiment # 2
By the end of the lab we will be able to:
• Examine a rock sample and determine if it is a sedimentary, metamorphic, or igneous rock.
• Define the terms used to describe the textures of the different sedimentary metamorphic or igneous rock.
• Name the common minerals found in most common types of sedimentary metamorphic or igneous rock.
• Use a classification key to identify rocks. • Recognize and name some of the common rocks.
Rocks and Rock Cycle
• Rocks - most are made up of mixtures of minerals.
• Some are made up of primarily one mineral. – Ex limestone is made up primarily made-up of
calcite.• Rock cycle - The process that transforms one
rock type into another.
Rocks
Igneous SedimentaryMetamorphic
Igneous
• Form either underground or above ground.
• Underground - they form when molten rock, called magma, deep within the earth becomes trapped in small pockets.
• Aboveground they form when volcanoes erupt, causing magma to rise above the earth's surface.
• As these pockets of magma cools, it becomes igneous rocks.
• Molten rock below ground is magma and above ground is called lava.
Igneous
Sedimentary Rocks
• Little pieces of our earth have broken down and worn away.
• How? - They are eroded down by wind and water.
• These little bits of our earth are washed downstream where they settle.
• Layer after layer are pressed together until the bottom layers slowly turn into rock.
Metamorphic Rocks
• They have "morphed" into another kind of rock.
• These rocks were once igneous or sedimentary rocks.
• They are under tons and tons of pressure, which fosters a build up of heat; this causes them to change.
Rock Cycle
Texture Vs. Composition
• We can identify types of rocks by describing their texture and composition.
• Texture - not how it feels but its cooling history.
• Composition - what type of minerals are present.
Types of Texture
• Coarse Grained• Fine Grained• Porphyritic• Glassy
Coarse Grained
• The longer the cooling time, the coarser (larger) the crystals present.
• This occurs inside the Earth.
• Coarse crystals can be seen without a microscope.
Fine Grained
• This occurs when the the rock is cooled rapidly. The shorter the cooling time the (finer) the crystals will be.
• This occurs near or on the Earth’s surface.
• Fine crystals can not be seen without a microscope.
Porphyritic
• Two different size crystals thus different rates of cooling.
• This occurs when the rock is cooling, it is pushed upwards where the rock cools faster.
Glassy
• No crystals develop because of very rapid cooling.
• Lack of crystals causes the rock to have a glassy appearance.
• Can also be a frothy color.
Color
• Mineral composition is the cause of the color change. We will only talk about
• Light
• Intermediate
• Dark
Types of Feldspar
• Potassium feldspar - contains potassium, pink in color.
• Also called Kspar from Potassium (K) Silicate (s) and feldspar (par) thus Kspar
• Plagioclase feldspar – will contain either sodium, calcium or a mixture of both.
Chart on pg 26
• From left to right the color and concentration of iron and magnesium increases.
• As we travel left to right the silica concentration decreases, and the magnesium concentration increases.
Light Color
• In the Felisic group
• Contains 0-15% dark minerals
• Contains potassium feldspar
• High concentration of potassium approximately 60-80%
• They will have a pink color.
Intermediate Color
• Mixture of light and dark colored minerals.
• Contains 15-45% dark minerals.
• Contains a percentage of plagioclase feldspar.
• Also called andesitic because they were first found in the Andes mountains.
Dark Color
• Contains 45-85% dark minerals • Contains Iron and Magnesium compounds.• High concentrations of Olivine, Pyroxene,
and Amphibole. • Also called Feromags.• Fe-iron, mag - magnesium
Work to be completed:
• Complete Chart on pg 27 using chart on pg 26.
• Start chapter Summary pg 35 questions 1-10
• Do not turn work in; it will be collected next week when we complete the second half of this lab.