Guided Notes for Igneous Rocks

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Guided Notes for Igneous Rocks

• Chapter 5, Section 1

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1) How are igneous rocks formed?

• Igneous rocks are formed from the crystallization
  of magma as it cools.

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2) What is lava?

• Lava is magma that flows out onto Earths surface.

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3) What are extrusive igneous rocks?

• Extrusive rocks are fine-grained igneous rocks
  that cool quickly on the Earths surface.

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4) What are intrusive igneous rocks?

• Intrusive rocks are coarse-grained igneous rocks
  that cool slowly beneath the Earths surface.

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5) What is magma?..

• Magma is a slushy mixture of molten rock, gases,
  and mineral crystals.
• Elements found in magma include oxygen, silicon,
  aluminum, and iron

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6) Why is silica an important magma compound?

• Because silica is the most abundant compound in
  magma, it has the greatest effect on magma
  characteristics.

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7) What are the 3 classes of igneous magma, and
how

• The 3 classes of magma are basaltic, andesitic,
  and rhyolitic.
• They are classified according to their silica
  content.

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8) At what temperatures do rocks melt?...

• Rocks melt at temperatures between 800C and
  1200C.
• These temperatures are found in the upper mantle
  and lower crust.

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9) State the four factors that affect magma
formation

1. temperatureincreases with depth in the Earths
   crust
2. Pressureas pressure on a rock increases, its
   melting point also increases
3. Water contentas water content increases, melting
   point decreases
4. Mineral compositionoceanic crust is rich in iron
   and magnesium and melts at higher temperatures
   than continental crust, which is rich in aluminum
   and silicon

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10) Explain why magma is often a slushy mix of
crystals

• Because different minerals have different melting
  points, not all parts of a rock melt at the same
  time. Thus, this partial melting is why magma is
  slushy.

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11) What is fractional crystallization

• When magma cools, it crystallizes in the reverse
  order of partial melting. Fractional
  crystallization is the process by which the first
  minerals to crystallize from magma are the last
  to melt during partial melting.

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12) Name 4 properties by which geologists
classify igneous rocks.

• Intrusive or Extrusive
• Mineral Content
• Grain Size
• Texture

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13) Describe the mineral composition of the 3
major groups..

• Felsichigh silica content, contain quartz and
  feldspar crystals (ex. Granite)
• Maficlow silica content, rich in iron and
  magnesium (ex. Gabbro)
• Intermediatemoderate amount of silica, contains
  biotite, amphibole, pyroxene (ex. Diorite)

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14) Why do some igneous rocks have large mineral
grains

• When magma cools slowly beneath Earths surface,
  large mineral crystals may form. These are
  intrusive rocks.
• Extrusive rocks have no visible grains because
  they are made from lava that cooled too quickly
  for crystals to form.

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15) What is porphyritic texture

• Porphyritic texture forms when slowly cooling
  magma suddenly cools rapidly.
• This forms a rock with large, well-formed
  crystals surrounded by finer-grained crystals of
  the same mineral.

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16) What characteristics of igneous rocks make
them useful

• Interlocking grain textures give them strength
• They are resistant to weathering
• Granite is one of the most durable igneous rocks.

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17) Which minerals are often found in veins of
ore?

• Gold, silver, lead, copper, and quartz are often
  found in veins.
• Usually, these veins are found inside igneous
  intrusions.

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18) What is pegmatite, and give an example.

• Pegmatites are veins of extremely large-grained
  minerals, such as garnets, which occur as
  crystals.

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19) What are kimberlites?...

• Kimberlites are rare, ultramafic rocks, which are
  a variety of peridotite. They form under very
  high pressure and often contain diamonds.
• Ultramafic rocks are very high in iron and
  magnesium.