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.