The Wonders of . . . ROCKS!!

Rocks All rocks are formed from minerals. There are three (3) main classifications of rocks: 1. Igneous 2. Sedimentary 3. Metamorphic

These rocks are formed under different conditions and posses certain characteristics. The characteristics a rock has depends upon the condition in which it formed. The rock cycle illustration below shows the process that each rock type undergoes to form.

Igneous Rocks Igneous: Rocks formed by the crystallization of molten material inside (intrusive) or outside (extrusive) the surface of the earth. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Felsic rocks are light colored and have a low denisty. Mafic rocks are dark colored and have a high density.

Magma or Lava? When molten rock is inside the earth it is called magma When molten rock is outside the earth, it is called lava.

Intrusive/Extrusive Slow cooling = large crystals Fast cooling = Intrusive rocks have a coarse texture with large mineral particles because of slow cooling. Slow cooling = large crystals Extrusive rocks have small grains or a glassy texture due to fast cooling. Fast cooling = no crystals

The crystallization of igneous rocks is a complex and time consuming process The more time a crystal has to form, the larger the crystal will be. If a mineral has a short amount of time to cool, like lava that pours into water, no crystals will form; obsidian, or volcanic glass will be the result. If cooling takes more time, crystals will start to form, but most often will cool too quickly to form crystals large enough to see the without the help of a magnifying glass. If given a long enough time to cool, crystals will begin to form that are large enough to see with the naked eye.

Magma that is stuck underground (intrusive) will cool very slowly, because it is insulated by the surrounding rock. As this material cools, crystals will form that can be very large (porphyry = large crystals). Pegmatite is an igneous rock with very coarse (porphorytic) texture (>10mm ~ see the ESRT!) Igneous rocks are identified based on their texture, density, color, grain size and mineral composition. Texture is the size and arrangement of mineral crystals; NOT how it feels!!

Get a black Earth Science book off the shelf . . . In your lab groups: Open to page 68 Answer questions 3 – 8 in complete sentences; one sheet per group. NO GROUPS LARGER THAN FOUR!

Time for your IGNEOUS ROCK lab!! Go get your lab books, Lab 2-3 Pages 73 – 75 Complete your vocab ESRT Page 6

Sedimentary Rocks Sediments (broken bits of rock) are materials that have been transported by air, water or ice. Most sediments are rock, but some can be pieces of animals or plants, and even molecules dissolved in water. When these materials are deposited, they form loose layers, and are then changed into rock layers.

Sedimentary rocks are formed from a variety of sediments. Sediments can range from clay (tiny particles) up to cobbles (very large particles) Check page 6 of your ESRT !! The main difference between clastic rocks and chemically formed rocks is the clastic rocks have obvious fragments whereas the chemical rocks appear to be homogenous or monomineralic.

Chemically formed rocks (evaporates) form when water containing dissolved particles evaporates, leaving the precipitate behind. Clastic sedimentary rocks form from the process of cementation, compaction and lithification. Sediments are deposited in layers, compacted by pressure and cemented by natural processes.

Types of sedimentary rocks: Clastic: Made up of fragments. Sediments are cemented (glued together) and compacted (pressed together) by burial. The compacted sediments then go through the process of lithification (hardened into layers)

Organic: Contains remains of living organisms. Animal or plant remains make up organic rocks. Coal is made of squashed plants; fossil limestone is formed when animal skeletons sink to the bottom of the sea and collect.

Precipitate/Chemical Evaporate: During the process of precipitation, water evaporates and leaves behind solids that were dissolved in the water. This process produces rock salt, rock gypsum and some limestones.

Most sedimentary rocks are formed by deposition in shallow seas, oceans and lakes. They are laid down in flat layers (A great identifying feature . . .) and sometimes contain fossils.

Some sedimentary rocks form a veneer, which is a thin covering or layer caused by the products of weathering and erosion from higher elevations being transported and deposited over large areas. Other sedimentary rocks are fossiliferous; meaning they contain a lot of fossils.

Sedimentary rocks are identified based on: How they are formed (clastic or chemical) Grain size (clay  cobbles) Mineral composition

ESRT ~ Page 7

Get a black Earth Science book off the shelf . . . In your lab groups: Open to page 74 Answer the following questions in complete sentences; one sheet per group. 9a 10a 11 a & b 13 – 16 NO GROUPS LARGER THAN FOUR!

Time for your SEDIMENTARY ROCK lab!! Go get your lab books, Lab 2-4 Pages 77 – 79 Complete your vocab

Rocks Metamorphic

Metamorphic Rocks Metamorphic rocks are formed by changing any pre-existing rock by exposure to heat and/or pressure. When heat and/or pressure is applied, recrystallization occurs. Recrystallization is the formation of new mineral crystals from pre-existing mineral crystals. (Breaking bonds and reforming new bonds – often creating new minerals)

Slate Foliation is banding of mineral concentrations and can take on several different forms. Slaty Foliation: Microscopic layers Schistose Foliation: Macroscopic layers with needle-like crystals. Gneissic Foliation/Texture: Macroscopic bands of minerals Schist Gneiss

Together, this heat and pressure will result in some sort of deformation. Often, rocks seem to have bands that are twisted and turned, resulting from metamorphosis of sedimentary rocks. Heat: When heat is applied to rock, it causes the minerals in the rock to expand and move apart. If heated enough, it may break the bonds and begin to form new minerals. Pressure: Pressure has the opposite effect of heat; it pushes the atoms of rocks together.

Therefore, during metamorphosis (adding heat and/or pressure), the size, spacing, and shape of the grains are changed. They may fuse due to heating and create brand new, exotic crystals.

Shale + pressure = Slate Increased density; Pressure, which forces the grains closer together, can cause the volume to decrease, while the mass remains the same. The density of the rock increases. Shale + pressure = Slate

Types of metamorphism: Contact: Contact metamorphism results in metamorphism by primarily heat over small, concentrated areas (generally as a result of contact with magma). Rocks tend to have a lower density due to expansion from heat. Regional: Regional metamorphism results in metamorphism by primarily pressure spread over broad areas of Earth’s crust; usually resulting in higher density rocks like slate, phylite, schist and gneiss.

Fossils are rarely found in metamorphic rock because of the heat and/or pressure they undergo. If fossils are present, they appear distorted and squished.

Some metamorphic rocks are very similar; like marble and quartzite Some metamorphic rocks are very similar; like marble and quartzite. The only way to differentiate between them is to perform and acid test to see if calcite is present. If calcite is present, it’s marble, if not, it’s quartzite. The minerals in metamorphic rocks will rearrange in layers because they tend to sort by density when they are heated. Quartzite forms from the metamorphism of its parent rock, quartz sandstone. When heat and/or pressure is applied, it causes the parent rock to become more dense and resistant to weathering.

Metamorphic rocks are identified based on foliation, mineral composition and type of metamorphism.

Time for your METAMORPHIC ROCK lab!! Go get your lab books, Lab 2-5 Pages 81 – 83 Complete your vocab ESRT Page 7

A few more key terms: Aggregate: Composed of a mixture of minerals. Weathering: The process of breaking down rock into fragments/sediments. Erosion: The process of transporting weathered materials.

Stratification: Formed and/or deposited in layers. Vesicular: Contains gas pockets.

Rock Summary: Rocks vary in color and type based on how they are formed and their mineral composition. A rock’s texture indicates the size of the mineral grains – NOT how it feels. Igneous rocks are identified based on grain size. Igneous rocks form from the solidification of molten rock, therefore, there will be no fossils. Sedimentary rocks are identified based on grain size and shape. Fossils are found in sedimentary rocks. Metamorphic rocks form from changing existing rock by heat and/or pressure. They exhibit banding or appear folded and/or layered. Any fossils present will appear distorted.

Which brings us full circle back to the rock cycle . . .