IGNEOUS ROCKS Igneous rock forms when magma cools and forms crystals

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IGNEOUS ROCKS Igneous rock forms when magma
cools and forms crystals
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CLASSIFICATION

• INTRUSTIVE EXTRUSIVE
• Plutons Volcanic
• Batholith
• Laccolith
• Sill
• Dike

Volcanic rocks are named according to both their
chemical composition and texture.
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• Intrusive Cool below the surface
• Extrusive Cool at the surface

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Cooling Temperature is one of the factors that
controls the type of igneous rock that forms
Bowen determined that specific minerals form at
specific temperatures as a magma cools. (The
higher temperatures associated with mafic and
intermediate magmas, lower associated with fesic)
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Slow cooling rate Large crystalsFast cooling
rate Small crystals

• Intrusive rock cools slowly, at depth, where
  the overlying rocks have had an insulating
  effect, therefore they have larger crystals.
• Extrusive rock has cooled quickly on the
  surface of the Earth, on land or on the ocean
  floor, and so crystals have little time to form
  and are therefore small.

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Composition of Magma

• We know from the study of modern volcanoes and
  from ancient igneous rocks that a wide range of
  different types of magma are possible.

• Similar to the Earth's crust as a
  whole, almost all magma contains oxygen as the
  most abundant constituent (silicon is second).

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• Pyroclastic rocks commonly associated with
  explosive volcanic activity Pyroclasts of
  different sizes are classified as volcanic bombs,
  lapilli and ash.
• Three modes of transport can be distinguished
  pyroclastic flow, pyroclastic surge, and
  pyroclastic fall.
• Phenocryst A conspicuous, usually large, crystal
  embedded in porphyritic igneous rock

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TEXTURES

• Two basic classifications based on crystal size
• Aphanitic (fine-grained) Phaneritic
  (coarse grained)
• Second level (sub-classifications)
• Porphyritic A combination of slow cooling where
  large crystals called phenocrysts are formed,
  along with a period of rapid cooling forming a
  finer grain matrix in which the phenocrysts are
  imbedded.
• Glassy Very fast cooling forming smooth
  appearance with conchoidal fracture.
• Frothy/Cellular/Vesicular Gas charged magma
  cools quickly and produces a foam-like glass
• Pyroclastic Fragments from explosive igneous
  activity set in volcanic ash. Can be large
  fragments or fine grained.

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Volcanic gas

• Magma contains dissolved gases that are released
  into the atmosphere during eruptions.
• Gases are also released from magma that either
  remains below ground (for example, as an
  intrusion) or rises toward the surface. In such
  cases, gases may escape continuously into the
  atmosphere from the soil, volcanic vents,
  fumaroles, and hydrothermal systems.
• The most common gas released by magma is steam
  (H2O), followed by CO2 (carbon dioxide), SO2
  (sulfur dioxide), (HCl) hydrogen chloride and
  other compounds.

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Potential effects of volcanic gases

• The volcanic gases that pose the greatest
  potential hazard to people, animals, agriculture,
  and property are sulfur dioxide, carbon dioxide,
  and hydrogen fluoride.
• Locally, sulfur dioxide gas can lead to acid
  rain and air pollution downwind from a volcano.
• Globally, large explosive eruptions that inject
  a tremendous volume of sulfur aerosols into the
  stratosphere can lead to lower surface
  temperatures and promote depletion of the Earth's
  ozone layer.

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Volcanic Gases

• Because carbon dioxide gas is heavier than air,
  the gas may flow into in low-lying areas and
  collect in the soil.
• The concentration of carbon dioxide gas in these
  areas can be lethal to people, animals, and
  vegetation.
• A few historic eruptions have released
  sufficient fluorine-compounds to deform or kill
  animals that grazed on vegetation coated with
  volcanic ash fluorine compounds tend to become
  concentrated on fine-grained ash particles, which
  can be ingested by animals.

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Currently Active Volcanoes

• http//www.geocodezip.com/v2_activeVolcanos.asp