Mr. Gessler

"marble is nice but don't take it for granite.- D.M  "

Rock Formation

devils_tower_md_wht.gif

Photo glossary of volcano terms

Rocks are naturally occurring solids made of minerals. The rocks texture is the size, shape and arrangement of the mineral crystals that the rock is composed of.

 WHAT KIND OF ROCKS ARE THESE?

Volcanoes

Mt. Rainier

Mount St. Helens National Volcanic Monument

Mount Saint Helens Imagery high-res

Photos of Mount Saint Helens

Blowdown

People of Pompeii

 

 

http://geology.asu.edu/jfarmer/archived_classes/glg335-fall02/RELDATIN.PPT powerpoint

 http://www3.interscience.wiley.com:8100/legacy/college/skinner/0471152285/ppt/ch04.ppt igneous rocks

 

Great Animations http://www.classzone.com/books/earth_science/terc/navigation/visualization.cfm

Clastic depositinal environments

Observe an animation of volcanism at a subduction zone.
 

Observe an animation of volcanic islands forming over a hot spot.
 

Observe how sediments are deposited.
 

Examine rocks from a satellite view and zoom in to a microscopic view.
Observe an animation of clastic sedimentary rocks forming.
 

Observe an animation of metamorphic rocks forming.
 

Observe how fossils can form.
 

Observe an animation showing the formation of an unconformity.
 

There are three groups of rocks, differing in how the rocks were formed:

  1. Igneous rocks- formed by liquid magma/ lava that cooled and solidified.
  2. Sedimentary rocks- rocks composed of fragments/ sediments of weathered rocks.
  3. Metamorphic rocks- rocks that have been altered by extreme pressure and heat, BUT did NOT melt.

 

I.                   Sedimentary Rocks

  1. Formation
  1. Cementation- when larger sediments (sand and pebbles) are cemented together by minerals that have precipitated out of solution. 11-1A,B

  1. Compression/ Compaction- when small particles such as clay or colloids are compressed together under pressure due to the water and the sediments above they can form rocks like the diagram labeled  11-1C
  2. Chemical action- when ionic or dissolved substances precipitate out of a solution they can form a monomineralic rock such as HALITE, CHEMICAL LIMESTONE or GYPSUM. Usually this is due to the evaporation of seawater. Upstate NY has huge salt deposits that formed in this manner. These rocks are called EVAPORITES or CHEMICAL SEDIMENTARY ROCKS.
  3. Biological processes- some sedimentary rocks are formed when organisms die and are buried. Clams and corals extract dissolved CaCO3  (limestone = calcite)directly from seawater to make their shells. When they die and sink to the bottom they form huge deposits of limestone (CaCO3) Calcite.
  4. FORMATION OF FOSSILS
  5. The end of the cretaceous
  6. Observe an animation showing the formation of an unconformity. an unconformity is when existing rocks are eroded and new materials are formed on top of this erosional surface.

 

  1. Characteristics of Sedimentary Rocks
  1. Clasts are rock particles. Sedimentary rocks made of rock fragments are called CLASTIC SEDIMENTARY ROCKS. Looking at a clastic rock sediments are easily observed.
  2. Some clastic sedimentary rocks have a large range in particle sizes. Sizes range from clay to pebbles. See diagram 11-1A.
  3. Some sedimentary rocks are organic. They are composed of the remains of plants that died and decomposed long ago in environments WITHOUT oxygen. Coal is an example of a biological sedimentary rock.
  4. One of the most prominent features of sedimentary rocks is that they have parallel layers or depositional beds called STRATA. Each strata may represent a season, a year, a millennium or some other time period in which deposition occurred.

 

 

 

 

  1. sedimentary rock identification
  1. USE the ESRT’s
  2. there are 2 main groupings: Clastic and Non-clastic
  3. Clastic rocks are named by the particle sizes
  4. Non-clastic rocks are named as either:
  1. Crystalline- rocks that formed when water evaporated
  2. Bioclastic- rocks formed from biological origins: shells, coal

Igneous Rocks-  CLICK THIS AND VIEW THE ANIMATION

 

 

Vocabulary:

  1. Intrusive- an igneous rock that forms from the slow cooling of magma.
  2. Plutonic rock- an igneous rock that forms when a magma intrudes into another rock and cools
  3. Extrusive- a rock formed by the rapid cooling of lava at earths surface. These are rocks formed of cooled lava, ash or volcanic dust.
  4. lava- molten rock exposed to earths atmosphere
  5. magma- molten rock beneath earths surface
  6. uniformitarianism- the earth was formed by the same forces that are presently occurring. “the present is the key to the past.” James Hutton 1795. the earth was not shaped by cataclysms but rather by slow steady forces that are acting today.
  7. Rock- a group of minerals that are bound together

Class Notes:

I.                     Uniformity of Processes

A.      Uniformitarianism- James Hutton 1795

1.       The geologic processes now at work were also active in the past

2.       the present geological features were formed by the same processes at work over very long periods of time

II.                   Three Groups of Rocks

A.      Igneous- formed by the cooling and hardening of molten rock from inside the earth.

B.      Sedimentary- rocks that form when rock sediments are hardened and cemented in layers.

C.      Metamorphic- rocks that form when existing rocks are changed by heat and pressure. No melting occurs.

III.                  Igneous rocks

A.      Plutonic Rocks

1.       form underground where magma cools slowly

2.       plutonic rocks cool slowly and large crystals form

3.       plutonic rocks can only be seen when the earths surface wears away exposing them

4.       the minerals cool and interlock with one another as the material cools

 

B.      Volcanic Rocks

1.       These rocks form when molten lava pours on earths surface

2.       Volcanic rocks have very small crystals due to the rapid cooling

3.       volcanic rocks do not have very distinct mineral grains because the rapid cooling causes the grains to be small- microscopic

 

IV.                Kinds of Magma- there are two general types of magma. Both are hot solid solutions of silicates. They range in temperatures from 600°c- 1200°c

A.      Felsic Magma- light in color, low in density

1.       Is thick slow flowing and high in silica SiO2  (quartz is Silica)

2.       when Felsic magma hardens it forms rocks that are light in color

3.       the name Felsic is derived from the composition of the rocks. Felsic rocks contain feldspar minerals and silica  (feldspar+silica= felsic)

4.       Most plutonic rocks are felsic ex: granite

5.       felsic rocks contain high amounts of Aluminum (Al)

6.       felsic rocks have a low density

 

 

B.      Mafic Magma

1.       this magma has a high percentage of Fe, Mg, and Ca

2.       the magma is a thin and fast flowing fluid

3.       when this magma solidifies it forms dark colored low silica rocks

4.       mafic rocks have many dark minerals like hornblende, biotite, olivine, pyroxene

5.       most volcanic rocks are mafic

6.       mafic rocks have a high density

 

V.                  Textures of igneous rocks

A.      texture of a rock depends on the size, shape and arrangement of a minerals crystals. Textures range from glassy smooth to coarse.

B.      Crystal size- the most important factor affecting texture.

1.       the crystal size is dependent on the cooling rate

2.       when the rock is liquid the atoms are free to move around and collect, forming large crystals

3.       when a rock cools rapidly crystals can not grow

4.       the amount of gas dissolved in a magma affects crystal size

a.       magma that has a lot of dissolved gas causes the elements to move around

b.       a high percentage of dissolved gases helps crystals to grow faster

c.       crystals grow larger in a relatively short time

5.       Magmas trapped deep below the earths crust cool very slowly and have large mineral grains of uniform size.

6.       if cooling is very rapid the magma turns into volcanic glass

 

VI.                Porphyritic Texture- an igneous rock that has two distinct crystal sizes.

1.       the large crystals are called phenocrysts

2.       the smaller background crystals are the rock matrix

 

VII.               Igneous rock families

A.      The Granites- light colored, felsic mainly orthoclase feldspar and quartz

B.      Gabbro- dark colored mafic rocks mainly olivine, pyroxene

C.      Diorite- has a color in between gabbro and granite

 

 

Name__________________________Date_________ period_____

Lab Quiz 2-3 Igneous Rock Identification                “Rocks of Fire”

10 questions. Answer using complete sentences, or else!

 

 

  1. There are two rocks. Rock “x” has crystals larger than 1.0cm. The second rock  “y” has microscopic crystals. Explain which rock cooled the fastest and how you came to this conclusion.
  1. Which rock is considered a plutonic rock, the rock with small-microscopic crystals or a  rock with very coarse crystals larger than 1cm?
  1. Explain what magma type will flow faster and why it flows faster. Describe the silica content in both magmas.
  1. A rock is composed of a fine pinkish matrix. Within this material there are larger crystals. What is the name of this texture?
  1. What is the name of a rock that has the following minerals present: potassium feldspar, quartz, biotite, and amphibole. The rock appears black with a non-crystalline texture.
  1. What does vesicular means.
  1. Pumice floats in water. Explain why
  1. How is rhyolite different from granite?
  1. How do mafic and Felsic rocks differ? Describe their composition and other important properties.

10. Is it likely that a fossil will be found in an igneous rock? Explain logically why or why not.

 

 

 

 

 

Metamorphic Rocks

 

Metamorphism means "changed form". 

Stress & Strain

Stress is a force applied over an area. One type of stress that we are all used to is a uniform stress, called pressure. A uniform stress is a stress wherein the forces act equally from all directions. In the Earth the pressure due to the weight of overlying rocks is a uniform stress, and is sometimes referred to as confining stress.
 

 

THEY DO NOT FORM BY MELTING!

Agents of Metamorphism

Changes occur because of:

bulletHeat
bulletPressure
bulletChemical fluids

Rocks adjust to become more stable under new, higher temperatures and pressures.

1.      Heat

There are several sources of heat for metamorphism.

    1. Geothermal gradient
      Temperature increases with depth.
    2. Ultimate source of the heat? Radioactive decay.

Increase of temperature and pressure with depth causes Regional Metamorphism
Heat may come from large bodies of molten rock rising under a wide geographic area.

    1. Intrusions of hot magma can bake rocks as it intrudes them. Lava flows can also bake rocks on the ground surface.

Lava or magma in contact with other rock causes Contact Metamorphism.

Hornfels is a common contact metamorphic rock.

2.      Pressure

    1. Burial Pressure. Pressure increases with depth due to the weight of the overlying rocks. A cubic foot of granite weighs 167.9 pounds. Increase of pressure and temperature with depth causes Regional Metamorphism.

Regional metamorphism occurs at depths of 5 - 40 km.

    1. Tectonic pressures associated with convergent plate boundaries and continental collision also cause Regional Metamorphism.
    2. Pressure along fault zones causes Dynamic Metamorphism, the crushing and ductile flow of rock.

Rocks formed along fault zones are called mylonites.

3.      Chemical Fluids

In some metamorphic settings, new materials are introduced by the action of hydrothermal solutions (hot water with dissolved ions). Many metallic ore deposits form in this way.

    1. Hydrothermal solutions associated with magma bodies
    2. Black smokers - Sea water percolates through newly formed oceanic crust, dissolving out metallic sulfide minerals. The hot sea water rises along fractures and pours from vents in the seafloor as black clouds of dark mineral-rich water. Sulfide minerals (such as pyrite, sphalerite, and galena) and copper precipitate when the hot water comes in contact with cold sea water.

How do rocks change?

Metamorphism causes changes in:

    1. Texture
    2. Mineralogy

Texture

The processes of compaction and recrystallization change the texture of rocks during metamorphism.

    1. Compaction
      bulletThe grains move closer together.
      bulletThe rock becomes more dense.
      bulletPorosity is reduced.
      bulletExample: clay to shale to slate
    2. Recrystallization
      Growth of new crystals. No changes in overall chemistry. New crystals grow from the minerals already present.

A preferred orientation of minerals commonly develops under applied pressure. Platy or sheet-like minerals such as muscovite and biotite become oriented perpendicular to the direction of force. This preferred orientation is called foliation.

Metamorphic Textures

    bulletFoliation is a broad term referring to the alignment of sheet-like minerals. Types of foliation:
    bulletSchistosity - alignment of large mica flakes, as in a mica schist derived from the metamorphism of shale.
    bulletSlaty cleavage - alignment of very fine-grained micas, as in a slate derived from the metamorphism of shale.
    bulletPhyllitic structure - alignment of fine-grained micas, as in a phyllite.
    bulletGneissic banding - segregation of light and dark minerals into distinct layers in the rock, as in a gneiss.
    bulletLineation refers to the alignment of elongated, rod-like minerals such as amphibole, pyroxene, tourmaline, kyanite, etc.
    bulletNon-foliated or granular metamorphic rocks are those which are composed of equidimensional grains such as quartz or calcite. There is no preferred orientation. The grains form a mosaic.

Examples: quartzite derived from the metamorphism of quartz sandstone, and marble derived from the metamorphism of limestone or dolostone.

The foliated metamorphic rocks

As shale is subjected to increasing grade of metamorphism (increasing temperatures and pressures), it undergoes successive changes in texture associated with an increase in the size of the mica grains.

    1. Slate - very fine grained rock. Resembles shale. Has slaty cleavage which may be at an angle to the original bedding. Relict bedding may be seen on cleavage planes. Often dark gray in color. "Rings" when you strike it. (Unlike shale, which makes a dull sound. Temperature about 200 degrees C; Depth of burial about 10 km.

    1. Phyllite - fine-grained metamorphic rock. Has a frosted sheen, resembling frosted eye shadow. This is no coincidence. Cosmetics commonly contain ground up muscovite (ground to a size similar to that occurring naturally in phyllite.)

 

 

    1. Schist - metamorphic rock containing abundant obvious micas, several millimeters across. Several types of schist may be recognized, based on minerals which may be present:
      bulletmica schist
      bulletgarnet schist
      bulletchlorite schist
      bulletkyanite schist
      bullettalc schist

    1. Gneiss - (pronounced "nice") - a banded or striped rock with alternating layers of dark and light minerals. The dark layers commonly contain biotite, and the light layers commonly contain quartz and feldspar.

 

 

 

The non-foliated (and weakly foliated) metamorphic rocks

    1. Marble - fizzes in acid because its dominant minerals is calcite (or dolomite). The parent rock is limestone (or dolostone).

    1. Quartzite - interlocking grains of quartz. Scratches glass. The rock fractures through the grains (rather than between the grains as it does in sandstone). The parent rock is quartz sandstone.

    1. Metagraywacke - metamorphosed graywacke or "dirty sandstone".
    2. Metaconglomerate and stretched pebble metaconglomerate - the parent rock is conglomerate. The clasts are fairly easily recognized. May be more difficult to recognize if the clasts have been stretched.
    3. Hornfels - A fine-grained, tough, dense, hard, massive rock. Usually (but not always) dark in color. Finer grained than basalt, which it may superficially resemble. This rock forms through contact metamorphism. The parent rock is commonly siltstone or basalt, but may be other types of rock.
    4. Serpentinite - A dark green, dense, tough, massive, hard rack. May contain veins of asbestos. The parent rock is peridotite, an ultramafic rock.

    1. Soapstone (sometimes called steatite) - a soft, easily carved rock with a slippery feel because it contains talc and chlorite. The parent rock is peridotite (ultramafic), probably with more water associated with it than in the formation of serpentinite. Example - Soapstone Ridge southeast of Atlanta.
    2. Metabasalt (sometimes called greenstone if massive and green, or greenschist if foliated and green) - the green color comes from chlorite (soft and bluish green) and epidote (pea green). The parent rock is basalt. The grade of metamorphism is LOW.
    3. Amphibolite - Abundant amphibole is present; may be lineated. Usually black. The parent rock is basalt. The grade of metamorphism is HIGH. Has been subjected to higher temperatures and pressures than metabasalt, greenstone, or greenschist.
    4. Mylonite - A dynamic metamorphic rock which forms along fault zones.


Mylonite along the Linville Falls Fault, Linville Falls, NC. Relatively undeformed conglomeratic quartzite lies above the layered mylonite zone.

Mineral changes in metamorphic rocks

    1. Recrystallization - rearrangement of crystal structure of existing minerals. Commonly many small crystals merge to form larger crystals, such as the clay in shale becoming micas in slate, phyllite, and schist.

Note the chemical compositions of clay and muscovite.

Also, fine-grained calcite in limestone recrystallizes to the coarse-grained calcite mosaic in marble.

    1. Formation of new minerals - there are a number of metamorphic minerals which form during metamorphism and are found exclusively (or almost exclusively) in metamorphic rocks:
      bulletGarnet - dark red dodecahedrons (12 sides)
      bulletStaurolite - brown lozenge-shaped minerals, commonly twinned to form "fairy crosses". State mineral of Georgia.

      bulletKyanite - sky blue bladed minerals with differential hardness. Scratch lengthwise with a knife or nail, but not sideways.

      bulletChlorite - dark bluish green, soft. Fe, Mg
      bulletTalc - white or pale green and soft.
      bulletGraphite - metamorphosed carbon
      bulletTourmaline - commonly black. Forms elongated crystals with a rounded triangular cross-section. Can see at Stone Mountain.
      bulletAsbestos - fibrous mineral. Commonly light greenish. Occurs in veins (seems to fill a crack) with the fibers oriented perpendicular to the edged of the vein. Associated with lung diseases. Mesothelioma and asbestosis. Found in serpentinite. "Serpent rock" name due to snake-like veins of asbestos.
      bulletMicas - muscovite (silvery), biotite (dark brown), phlogopite (light brown)
  1. Metamorphic rocks are formed by:
    1. Cooling and solidification of magma
    2. Compression and cementation of sediment
    3. Recrystalization of heated rock
    4. play-doh and clay

 

  1. Which of the following does not create a metamorphic rock?
    1. growth of mineral crystals
    2. melting and solidification
    3. compression within the earth
    4. intense heating without melting

 

  1. If a rock displays bands of similar minerals, the grain size is coarse and the rock appears to have been folded, what type of rock is it?
    1. marble
    2. hornfel
    3. gneiss
    4. quartzite

 

 

  1. How does the metamorphic rock gneiss differ from the igneous rock granite?
    1. the minerals are different
    2. the gneiss never quite melted
    3. granite is made of rounded particles from sediment deposition
    4. the granite shows distinct banding

 

 

  1. Which 2 rocks would be separated by a zone of contact metamorphism?
    1. shale and limestone
    2. granite and basalt
    3. shale and basalt

 

  1. According to the NYS ESRT’s what rock results from the metamorphism of sandstone?
    1. concrete
    2. granite
    3. sandstone
    4. quartzite
    5. anthracite coal

 

  1. What is the name of a foliated rock with medium grade metamorphism of mica crystals, feldspar and clay minerals?
    1. rock salt
    2. schist
    3. slate
    4. hornfels

 

  1. What is the proper order of metamorphism for the following rocks ( increasing in the degree of metamorphismJ)
    1. schist, shale, gneiss, slate
    2. slate, shale, schist, gneiss
    3. shale, slate, schist, gneiss
    4. gneiss, schist, slate, shale