Geology 102

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Geology 102

• Lab 3
• Rocks

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Rocks vs. Minerals

• What is the difference?

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What is a Rock?

• Naturally Occurring
• Mechanically Coherent Aggregate
• Composed of several minerals

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Rocks

• Rocks are the building blocks of solid earth
• Rocks can be grouped into three (3) general
  families
• Igneous (includes intrusive and extrusive)
• Intrusive cools within the earths surface
• Extrusive cools outside the earths surface
• Sedimentary
• Metamorphic

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Igneous Rocks

• Rocks which have solidified from magma or lava
  (hot liquid rock)
• Classified on the basis of light and dark
  minerals and crystal size
• Dark colored 1st to crystallize
• Medium colored 2nd to crystallize
• Light colored last to crystallize
• Coarse grained cooled slowly
• Fine grained cooled rapidly
• Glassy cooled extremely fast (ex. 12)

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What is a Phenocryst?

• In an igneous rock, when a large grain is
  completely surrounded by a fine grains

Phenocrysts
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Sedimentary Rocks

• Rocks that are formed from the erosion products
  of pre-existing rocks or from the remains of
  plants and animals
• Most common family of rocks on the earths
  surface
• Classified on grain size or type of plant or
  animal material
• Size of grains often related to the distance that
  the grains were transported
• Coarse short distances
• Fine - far distances

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Metamorphic Rocks

• Rocks produced by the alteration of other rocks
  (pre-existing) when exposed to extremely high
  temperatures and pressure (deep inside the earth
  or in contact with magma or lava) as well as
  chemical activity.
• Temperature ranges from 200oC 600oC
• Generated by volcanism or orogeny (mountain
  building)
• Classified on their minerals and foliation

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What is Foliation?

• The parallel alignment of the mineral grains

Alternating light and dark layers foliation
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The Rock Cycle

• A model of the interrelationships of the
  different rock types, the materials that they
  form, and the processes that produce the rocks.
• An alternative definition (and easier) is
• A series of events through which a rock changes,
  over time, between igneous, sedimentary, and
  metamorphic

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The Rock Cycle
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Lab Procedures

• Complete the table on page 25 of your lab book.
• To do this, use the rock descriptions on pages 19
  21 as well as the tables on pages 22 24
• Mark off Serpentinite (on page 21). You do not
  have this rock in lab, nor will you see it on the
  test.

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1 - Granite

• Igneous
• Large Crystals of quartz, feldspar, and mica
• Much of earths continental crust is composed of
  granite

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Granite outcrops of Yosemite National Park, Ca.
El Capitan
Half Dome
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2 - Conglomerate

• Sedimentary
• Rounded gravel-size grains
• Mostly quartz
• Generally formed in river channels

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3 - Slate

• Metamorphic
• Hard
• Has a smooth sheet-like surface
• Metamorphosed Shale

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4 - Diorite

• Igneous
• Large grains of feldspar and amphibole
• salt and pepper texture

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5 - Sandstone

• Sedimentary
• Sand-sized grains
• Formed in river channels, beaches, deserts, etc.

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Sandstone Arch in Arches National Park
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6 - Schist

• Metamorphic
• Parallelism of micas gives the rock a sheen (it
  is shiny)

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7 - Basalt

• Igneous
• Crystals too small to be seen
• Dark color
• Much of earths oceanic crust is composed of
  basalt

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8 - Shale

• Sedimentary
• Particles of mud
• May be finely layered
• May form in lakes, along flood plains of
  meandering rivers, or on the deep ocean floor

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Burgess Shale
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9 - Gneiss

• Metamorphic
• Coarse banding of light layers (quartz and
  feldspar) from dark layers (mica)

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10 - Limestone

• Sedimentary
• Composed of calcite
• Fizzes with dilute acid
• Usually has fossils
• Formed in shallow seas on or near reefs

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11 - Coal

• Sedimentary
• Black
• Shiny
• Sooty
• Low density
• Formed in tropical swamps

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12 - Obsidian

• Igneous
• Glassy
• Conchoidal fracture

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13 - Marble

• Metamorphic
• No foliation
• Composed of large crystals of calcite
• Fizzes with acid (might need to be scratched
  first)
• Metamorphosed Limestone

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14 - Pumice

• Igneous
• Looks like hardened foam with many buble holes
  (vesicles)
• Light weight

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Pumice floating in water
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15 - Chalk

• Sedimentary
• Composed of calcite and fizzes with acid
• Formed in the deep sea (composed of microscopic
  organisms)

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Chalk Mine in England
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16 - Quartzite

• Metamorphic
• No foliation
• Very hard
• Composed of large crystals of quartz
• Metamorphosed Sandstone

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17 - Rhyolite

• Igneous
• Phenocrysts present
• White, grey, or pink in color

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18 - Gabbro

• Igneous
• Large crystals of dark feldspar and other dark
  minerals (can have olivine in it)
• Color is usually dark green, dark grey, or almost
  black