ROCKS I What is a rock A rock

ROCKS I. What is a rock? • A rock is a mix of minerals, mineraloids, glass or organic matter. ALL rocks are made of 2 or more minerals. II. The Rock Cycle: the process by which rocks are formed over MANY years. It is a continuous repeating pattern. ESRT p. 6 • Changes back & forth among igneous, metamorphic, & sedimentary rocks • Erosion, weathering, compaction, & cooling can change them • Also changed by heat & pressure • The rock cycle has NO BEGINNING OR END!!

In Conclusion… • The rock cycle demonstrates the relationships among the three major rock groups • It is powered by the interior heat of the Earth • As well as earth’s momentum and… • The energy from the sun • It involves processes on the Earth’s surface as well as the Earth’s interior • It connects the “hydrologic cycle” with the “tectonic cycle”.

Classifying Rocks • Rocks are classified by how they formed and what • • • they’re made of There are 3 general classes of rocks Igneous Rocks…are formed when lava and magma crystallize to form solid rock Metamorphic Rocks…are formed when an existing rock is partially melted, squeezed, or both Sedimentary Rocks…are formed when sediments (sand clay, and silt) are compressed and become solid rock

III. Igneous Rocks • Formed by the cooling & solidification of magma & lava resulting in a rock w/intergrown crystals A. Magma: hot, melted rock beneath the earth’s surface (1400 o. C); usually found underground & can be forced up towards the surface (usually by volcanoes)

B. Lava • Molten rock from a volcano flowing onto the earth’s surface. This is above ground & cools faster than magma b/c it’s exposed to cooler temps than magma. • Both of these contain crystals…which are MINERALS!!

There are 2 Types of Igneous Rocks 1. Intrusive: magma cools beneath the earth’s surface. Intrusive: Inside the earth. • Indicated by larger mineral grains • Cooling below the earth’s surface is slower & allows the mineral grains to grow larger

Eg: Granite • Light-colored, coarsegrained, no pattern • Mostly quartz, feldspar, mica, and hornblende • Often used for buildings and monuments

2. Extrusive • Formed by lava that cools @ the earth’s surface • Cooling @ earth’s surface is faster, not allowing mineral grains & crystals to grow: smaller mineral grains than intrusive. Or, may have no grains – glassy appearance. • Extrusive: outside the earth’s surface.

Eg: Obsidian • Natural volcanic glass • Forms when lava cools very quickly • Usually dark, but small pieces may be clear • Fractures along curved (conchoidal) surface • Used as spear and arrow points, knives

Vesicular • Rock that contains gas pockets Scoria *** some igneous rocks don’t show crystal patterns. These rocks are referred to as glass.

C. Classification Based upon color & density, based upon magma type. 1. Basaltic: dense, heavy, & dark colored. Rich in magnesium (Mg) & iron (Fe); rocks that are formed from basaltic lava that flows directly from volcanoes. Continental crust. Basalt

Basalt • Dark-colored, fine- grained, extrusive • Formed where lava erupted onto surface • Most widespread igneous rocks • Found locally in the Palisades along west shore of Hudson River, Connecticut River valley

2. Mafic • Contains heavier elements resulting in a darker color & higher density. Rich in basalt & gabbro(Mg & Fe). Oceanic crust. Gabbro

3. Granitic/andestic light colored & lower density than basaltic Has much Si & O 2 Flows from volcano Andestic composition is between granitic &basaltic andesite 4. Felsic: light colored, rich in feldspar & silica, lower density ryholite • •

D. Mineral Classification in Rock Steps: ESRT rock ID 1. Find the rock on the Igneous Rock Identification Chart 2. Follow the column down to the composition part of the chart & read the minerals. 3. The actual % can be determined by marking the span of the mineral on another piece of paper & then using the scale of the side diagram.

IV. Sedimentary Rocks • Formed when sediments that were pressed or cemented together or when sediments ppt out of solution. A. Terms: • Sediments: loose material such as rock fragments, mineral grains &/or bits of organic material (plants, bones) are moved by wind, water, ice, or gravity.

• Weathering: the process that breaks rocks into smaller pieces • Erosion: the movement of weathered material

• Compaction: occurs when layers of small sediments become compressed by the weight of layers above them. Pressure from the top pushes down on the bottom.

Cementation: • process in which large sediments are glued together by minerals deposited between sediments. Water soaks thru the rock & soil, some minerals will dissolve & make sediments stick together.

Sedimentary Rock Layers • Often form layers • Older layers on the bottom – these were deposited FIRST • More sediments pile up, become compacted & cemented • Sometimes the layers are disrupted & the older ones are no longer on the bottom

B. Classification 1. Detrial or Clastic: detrial means to “wear away” Rocks made from other rocks broken down by weathering compaction & cementation. a) Clastic texture: “broken” texture b) Shape & size of sediments: clastic rocks are named according to the size & shape of their sediments: - conglomerate: well rounded sediments

- Breccias: sharp angles, not rounded - Concrete: gravel & grains

Grain size: boulders, cobbles, pebbles, sand, silt, & clay

2. Chemical Sedimentary Form when minerals ppt out from a solutionlike when seas or lakes evaporate a) Limestone: calcium carbonate (found in ocean waters) comes out of solution (crystals grow together) & are deposited on sea or ocean floors. b) Rock salt: lakes or seas evaporate, deposit the mineral halite; when mixed w/other minerals will form halite rock.

3. Organic • Formed from the remains of once living things or from life processes (therefore not WHAT? ? ) • Fossils are the main organic material from both plants & animals Limestone

How Sediments Travel 1. Particles are transported by wind & water & glaciers. Water moves the greatest amount of sediments. 2. Stream Transport: • Particles will become rounded & smooth as they bang & rub against each other= abrasion • The > the distance traveled, the smoother & rounder the particles become • The > the velocity of a stream, the > the particles they can transport

3. Deposition of Sediment occurs when a stream slows down… a) Enters a standing body of H 2 O b) When the gradient decreases 4. Deposition by a stream results in sorting of sediments= graded deposit a) The largest particles will be deposited 1 st – as the velocity decreases more, the smaller particles will be deposited further out into the body of H 2 O VID

Useful Sedimentary Rocks • Minerals, corals, & snails make the shells from the mineral calcite. When they die, shells accumulate on the ocean floor. • If the shell fragments are large, they’re called coquina

• If the shell fragments are microscopic, they’re called chalk • Coal: forms when pieces of dead plants are burned under other sediments in swamps & changed by microorganisms.

V. Metamorphic Rock Origin: rocks that change due to an increase in To & pressure or undergo changes in composition are called metamorphic rocks. These can also change from igneous, sedimentary, or other metamorphic rocks. A. Heat & Pressure: • rocks beneath the earth’s surface are under great pressure from overlying rock layers. Once heat & pressure hit a certain point it’ll turn to magma

• If the heat isn’t enough to cause melting, minerals will flatten out like a pancake (will show type of layering). • Any type of rock can become metamorphic Eg: granite (igneous) gneiss (metamorphic) Eg: addition of pressure: shale slate phyllite schist gneiss • Met rocks are NOT porous • They’re easy to split, have thin layers of alternating materials called banding, & are similar to the parent rock.

B. Classification: again, metamorphic rocks are formed from any of the 3 types of rocks due to heat & pressure. They can be classified by their texture: Foliated or Non-foliated

B. Classification 1. Foliated: when mineral grains flatten & line up in parallel bands, the met. rock has a foliated texture. Eg: Slate & gneiss

Foliated Textures • • Slatey • • Schistose -- looks like blackboard >>dull surface -- smooth, thin layering -- breaks into flat slabs >>referred to as slatey cleavage -- no mineral grains visible • • Phyllitic >>garnets, staurolites -- may have shiny appearance >>due to mica minerals • • Gneissic -- looks like waxed surface >>has a "sheen" to it -- may have little "waves" on surface >>referred to as -- distinct bands of minerals -- visible grains crenulations -- some small grains visible -- larger grains -- may look like igneous rock -- may have crude banding >>intensely distorted -- different minerals than schistose

2. Non Foliated: in some met. rocks, no banding occurs; the mineral grains change, grow, & rearrange, but do NOT form bands. Eg: marble

C. Types of Metamorphism • Contact- caused by igneous activity • Dynamic - aka cataclastic; associated with faults & earthquake zones • Regional- caused by tremendous pressures; associated with tectonic plate activity

1. Contact Metamorphism Igneous Intrusions • size and type of magma important - mafic magma hotter than felsic • Heat decreases away from magma • forms a zone of altered country rocks called Aureoles • Sometimes creates a metamorphic rock called a hornfels -in essence a “cooked” rock

2. Dynamic Metamorphism aka Cataclastic Metamorphism associated with Fault Zones Places where the Earth's crust ruptured Rock pulverized heat and pressure come from movement along the fault • resultant rock is known as a Mylonite • •

3. Regional Metamorphism • Most common form of metamorphism • caused by large scale forces - lithospheric plate collision • covers very large areas • metamorphic belts or zones • Zones are characterized by - Index Minerals that form under specific temperatures and pressures • metamorphic facies: The metamorphic facies are groups of Index Minerals compositions by which it can be recognized • commonly associated with shields: stable areas of crystalline rocks

Metamorphic Zones • Metamorphism is common along most plate boundaries like this.