How do rocks differ from minerals The physical

How do rocks differ from minerals? • The physical properties of a mineral are homogeneous (the same throughout the sample) • The physical properties of a rock are usually heterogeneous (they vary throughout the sample) because they’re usually made up of several minerals • Rocks are classified according to origin (how they form)

These minerals are all in this rock

Rock Classification – 3 major groups based on their methods of formation or origin 1. Igneous rocks … from cooling and solidification of lava or magma 2. Sedimentary rocks … from compacted and cemented sediments, or chemical precipitates or evaporites 3. Metamorphic rocks … meta (change) morphic (form) … rocks changed by heat and pressure – but remain solid

SEDIMENTARY ROCKS

Sedimentary Rocks • 80 % of Earth’s surface is covered with sediments and Sedimentary Rocks

What is sediment? ? q Broken pieces of rocks called CLASTS q Chemical precipitates ( dissolved solids come out of solution) q Organic fragments – shells, decayed plant matter – this is called BIOCLASTIC

Sedimentary Rocks form when sediments/clasts are transported to large bodies of water and are … Deposited in horizontal layers called beds or strata Buried Compacted – particles forced extremely close together because of the pressure of the overlying layers and water Cemented – glued together

Sedimentary Rocks q Sediments that are eroded settle to the bottom of the rivers, lakes, and oceans q Layer after layer of eroded earth is deposited on top of each other

Cementing Material (Glue) • Minerals precipitate out of solution to cement particles together. Cementing material is often quartz, calcite, and hematite Most Sedimentary Rocks form under large bodies of water, such as lakes, seas, and oceans

Horizontal layers deposited under water

Classification of Sedimentary Rocks • We classify sedimentary rocks depending on whether the sediments came from – Particles of other rocks (“land derived”) – Ions that have precipitated out of seawater (“chemically derived”) – Living organisms (“organically derived”)

Sand Composition Varies BUT TO BE CONSIDERED SAND THE GRAIN SIZE IS BETWEEN 0. 2 -0. 006 CM.

Sedona Sandstone

Sediments are pebbles, cobbles, and boulders rounded Breccia angular

Silt (0. 006 to 0. 0004 cms. SILTSTONE Sand (0. 2 to 0. 006 cms. ) SANDSTONE Clay (less than 0. 0004 cms. ) SHALE

Shale Source: Photograph © The Mc. Graw-Hill Companies, Inc. /Bob Coyle, photographer.

Sandstone Source: Photograph © The Mc. Graw-Hill Companies, Inc. /Doug Sherman, photographer.

2 TYPES OF TEXTURE q CRYSTALLINE FOR CHEMICALLY FORMED SEDIMENTARY ROCKS q BIOCLASTIC FOR ORGANICALLY FORMED SEDIMENTARY ROCKS q HOW USEFUL IS GRAIN SIZE? ?

CHEMICAL Sedimentary Rocks Sediment From Solution q All liquid water contains dissolved minerals. q These minerals precipitate (dissolved solids come out of solution/water) q Usually happens because of evaporation q They are monominerallic – consisting of intergrown crystals of just 1 mineral. q Form in shallow seas

ROCK SALT Intergrown crystals of just 1 mineral DOLOSTONE ROCK GYPSUM

ORGANIC Sedimentary Rocks Bioclastic Sediment LIMESTONE AND CORALS • Dissolved minerals taken out of solution by marine organisms for their hard parts (shells) can pile up on the seafloor when they die. • These fossil remains accumulate into a thick enough layer to form an “organic” sedimentary rock • Cement is commonly calcite ( bubbles with acid) COAL • Decayed plant remains

BIOCLASTIC LIMESTONE COAL CHEMICALLY PRECIPITATED LIMESTONE

Centralia Pennsylvania Coal Fire • http: //dlbtboces. org/webapps/portal/frameset. jsp? t ab=courses&url=%2 fbin%2 fcommon%2 fco urse. pl%3 fcourse_id%3 d_2495_1

Summary q Inorganic Land-Derived Sedimentary Rocks are identified by Texture or Grain Size q. Chemically and/or Organically Formed Sedimentary Rocks are identified by Composition What conditions control which Sedimentary Rock is formed? ? ?

THE SIZE OF THE GRAIN IS DETERMINED BY THE ENVIRONMENT OF FORMATION q HIGH ENERGY ENVIRONMENT Large particles Fast moving water – rivers, ocean waves q LOW ENERGY ENVIRONMENT Small particles Slow moving water – lake, bay, swamp

SEDIMENTARY ROCK WHERE IT WAS PUT TOGETHER CONGLOMERATE BRECCIA HIGH ENERGY SANDSTONE MEDIUM ENERGY SILSTONE LOW ENERGY SHALE VERY LOW ENERGY

Environment of Formation Ocean Derived Sedimentary Rocks help us understand our past geologic history There is evidence of climate change as well as lost species of plants and animals in Sedimentary Rocks

During the Cretaceous Period (about 120 mya) a shallow inland sea split North America. We know this by the Sedimentary Rocks deposited in the former shallow sea

Cretaceous Limestone Deposits in Kansas

SALT AND GYPSUM EVAPORATION q Bedrock of Salt and Gypsum around Buffalo q What type of environment would cause salt and/or gypsum to evaporate? q Ocean environment with hot temperatures

CHARACTERISTICS OF SEDIMENTARY ROCKS 1. Horizontal layers called beds or strata 2. Clasts are rounded and sorted because they have been moved by water 3. Ripple Marks 4. Mud Cracks 5. Fossils 6. Interconnected mineral crystals of 1 mineral (monominerallic)

HORIZONTAL LAYERS

A. SHALLOW WATER B. LOW ENERGY C. DIRECTION OF FLOW

MUDCRACKS ALTERNATING WET AND DRY CONDITIONS

Limestone - FOSSILS

IGNEOUS ROCKS

MAGMA VS. LAVA Magma – molten material BELOW the surface of the Earth Lava – molten material AT OR ABOVE earth’s surface

ENVIRONMENT OF FORMATION COOLING HISTORY MAGMA LAVA Intrusive – below the surface Extrusive - above the surface A pluton is a body or chamber Ejected from volcano of magma deep inside the crust. Rocks formed when magma Rocks formed when lava cools and solidifies are called INTRUSIVE (PLUTONIC) EXTRUSIVE (VOLCANIC)

EXTRUSIVE FEATURES VOLCANO - landforms generated when lava is released from the Earth’s interior through openings.

Magma Intrusive Features - Plutonic

Formation of Igneous Rocks q. COOLING AND SOLIDIFICATION OF MAGMA/LAVA q. INTERGROWN OR INTERCONNECTED SILICATE CRYSTALS IN A RANDOM PATTERN – NOT ORGANIZED

IGNEOUS ROCKS ARE CLASSIFIED BASED ON 2 MAIN CHARACTERISTICS • TEXTURE – MINERAL GRAIN SIZE • MINERAL COMPOSITION

What controls texture? How fast an igneous rock cools. What controls how fast an igneous rock cools? Where the rock is formed. slower cooling coarser crystals deep in ground

ESRT – TOP OF THE IGNEOUS ROCK SCHEME TELLS THE TEXTURE / GRAIN SIZE

Classification of Igneous Rocks – Texture or Grain Size Extrusive Intrusive Volcanic - LAVA Volcanic- LAVA Plutonic - MAGMA Extremely fast Fast Cooling cooling Slow Cooling Extremely slow cooling Non. Fine-grained crystalline Glassy vesicular (gas pockets) Coarsegrained Very Coarsegrained

EXTRUSIVE – VOLCANIC - LAVA • When lava cools extremely fast crystals have no time to form – JUST FROZEN IN PLACE RANDOMLY WHEN LAVA ENTERS ATMOSPHERE OR WATER • GLASSY – NON-CRYSTALLINE Non-vesicular Vesicular gas pockets

EXTRUSIVE – VOLCANIC - LAVA Lava that cools fast at or near the Earth’s surface Produces small crystals FINE-GRAINED TEXTURE not easily seen with the naked eye.

INTRUSIVE – PLUTONIC - MAGMA Magma that cools slowly deep underground produces large crystals COARSE-GRAINED TEXTURE easily seen with the naked eye.

INTRUSIVE – PLUTONIC - MAGMA EXTREMELY SLOW COOLING HAS ABNORMALLY LARGE CRYSTALS AND IS VERY COARSE.

What does granite bedrock exposed at the surface indicate?

COOLING HISTORY / GRAIN SIZE ALONE CANNOT NAME THE ROCK WE NEED TO KNOW COMPOSITION TEXTURE + COMPOSITION = ROCK CAN BE IDENTIFIED

THE BOTTOM OF THE IGNEOUS ROCK SCHEME TELLS YOU THE COMPOSITION TEXTURE + COMPOSITION CAN NAME ROCK

Igneous Rocks Consist of 7 Silicate Minerals Quartz Potassium feldspar Plagioclase feldspar Biotite mica Amphibole (hornblende) Pyroxene Olivine NO SINGLE IGNEOUS ROCKS IS MADE UP OF ALL 7 MINERALS

FELSIC VS. MAFIC FELSIC MAFIC “FEL” = FELDSPARS “MA” = MAGNESIUM “SIC” = SILICA “F” = IRON High % of quartz, feldspars, mica “IC” = SILICA High % of pyroxene, feldspars, amphibole DARKER IN COLOR LIGHTER IN COLOR LESS DENSE

FELSIC COMPOSITION COLUMN + COARSE TEXTURE ROW

IGNEOUS ROCK COMPOSITION FELSIC ROCKS – CONTINENTAL CRUST GRANITE – coarse-grained (continental crust) RHYOLITE – fine-grained OBSIDIAN - glassy and PUMICE - porous (vesicular). PEGMATITE - very coarse-grained

IGNEOUS ROCK COMPOSITION MAFIC ROCKS –OCEANIC CRUST GABBRO – coarse-grained BASALT – fine-grained (ocean crust) SCORIA – vesicular (gas pockets) VESICULAR BASALT – vesicular

IGNEOUS ROCK COMPOSITION INTERMEDIATE ROCKS MIXED FELSIC/MAFIC MIXED CRUST ANDESITE (named for Andes Mountains) – fine-grained 2 nd most abundant volcanic rock in Earth’s crust. DIORITE – coarse-grained

IGNEOUS ROCK COMPOSITION ULTRAMAFIC ROCKS – form from magma in ASTHENOSPHERE Dominated by Fe-Mg silicates, olivine and pyroxene. Very dark in color and dense Found at converging continental plate boundaries. Peridotite Dunite

INTRUSIVE EXTRUSIVE Granite Rhyolite Figure 4. 7 A MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE Andesite Diorite Intrusive vs. Extrusive

INTRUSIVE Gabbro EXTRUSIVE Basalt MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE Intrusive vs. Extrusive

Lava Field at Sunset Crater

WHAT GRAPH BELOW SHOWS AS TIME INCREASES THE SIZE INCREASES? A B

METAMORPHIC ROCKS

METAMORPHIC ROCKS META = CHANGE MORPH = FORM q Called the “Cinderella Rock” q Start with pre-existing rock and change to another rock – but these changes occur in the SOLID STATE

METAMORPHISM q Process by which igneous, sedimentary, or another metamorphic rock called the “parent rock” undergoes changes in minerals and texture

METAMORPHISM Occurs in rocks due to the effects of • High temperature (but not high enough to melt!) • High pressure

HEAT EFFECTS q Temperature increases with depth or contact with magma q Recrystallization – a process that forms new mineral crystals because the mineral is no longer stable at the new temperature • Changes to a new (high temperature) mineral

PRESSURE EFFECTS q Pressure increases with depth – weight of overlying rock (see page 10 ESRT) q Mineral crystals grow larger q Mineral crystals are more dense q Mineral crystals grow perpendicular to pressure q Mineral crystals are arranged in parallel layers – PRODUCES FOLIATION

FOLIATION q Pressure actually rearranges the minerals into parallel layers. q More pressure – minerals grow larger and recrystallize and separate into layers q Even more pressure – alternating layers of light and dark minerals called Banding

Random arrangement of minerals Organized arrangement of minerals - banding

Granite Intergrown crystals random pattern Gneiss Intergrown crystals Organized Pattern

2 Types of Metamorphism 1. Regional Metamorphism – Occurs over large areas where there is active mountain building a) Convergent plate boundaries 2. Contact Metamorphism – areas in contact with magma intrusions and/or lava extrusions

MOUNTAIN BUILDING

Classification of Regional Metamorphic Rocks q Composition is basically the same for all foliated rocks – parent rock is usually listed in comments section. q Type of texture and grain size determined by the amount of heat and pressure

GRADES OF METAMORPHISM LOW GRADE – LESS HEAT AND PRESSURE – SLATE HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS

Temperature q. Low-grade metamorphism: Occurs at about 2000 C to 5000 C. and pressure greater than 1, 000 atmospheres q. High-grade metamorphism: Occurs at > 5000 C

FOLIATED METAMORPHIC ROCKS

MICA SCHIST WITH GARNET MICA CRYSTALS BECOME LARGE AND SPANGLY

Grand Teton Gneiss

METAMORPHIC ROCKS WILL OFTEN BE DEFORMED BECAUSE OF INTENSE HEAT AND PRESSURE LOOK AT ROCK SYMBOL FOR GNEISS

A metamorphic rock exposed to too much heat will melt and become ? ? ? MAGMA

q Near magma chambers (plutons) q Rocks in “contact” with the magma are baked q New minerals are formed – recrystallization q Transition zone of contact metamorphism is usually relatively narrow baking the adjacent rocks

Contact Metamorphism – Baking the adjacent rocks

Symbol for Contact Metamorphism is a line with tick marks When limestone undergoes contact metamorphism what rock will it metamorphose into? Sandstone? ?

PARENT ROCK IN THE COMMENTS

LIMESTONE METAMORPHOSES INTO MARBLE

SANDSTONE METAMORPHOSES INTO QUARTZITE

Rock Classification Summary • If the rock looks “dirty” or contains fossils, it’s sedimentary • If the rock shows banding or folds or twists or mineral alignment, it’s metamorphic • If the rock is glassy or contains rounded crystals or gas pockets, it’s igneous

Rock Distribution • Sedimentary rocks are at or near the Earth’s surface because they require water to form • Igneous rocks are found near volcanoes and deep underground. • Metamorphic rocks are found deep within mountains, deep underground, and at transition zones between sedimentary and igneous rocks

ANY TYPE OF ROCK CAN BE CHANGED INTO ANY OTHER TYPE OF ROCK