Igneous Rocks

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Igneous Rocks!

• ESCI 518

http//volcano.und.nodak.edu/vwdocs/current_volcs/
current.html
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Igneous Rocks

• Form from melt (magma vs. lava)
• Classified based on composition and texture

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Igneous Rocks
http//www.veoda.com/search/click/smartframe.cgi?h
ttp//volcanoes.usgs.gov/Products/Pglossary/basalt
.html
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Composition of Igneous Rocks

• 95 of igneous rocks made of 6 silicate
  minerals (quartz, feldspar, mica, olivine,
  pyroxene, amphibole)

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Important to distinguish feldspars!
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Texture of Igneous Rocks

• Phaneritic (intrusive)
• Visible crystals
• Cooled slowly
• Aphanitic (extrusive)
• Crystals only visible under microscope
• Appear massive and structureless
• Cooled rapidly

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Granite
http//physics.uwstout.edu/geo/gallery/white_grani
te.jpg
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Granite
http//www.usoe.k12.ut.us/curr/science/sciber00/8t
h/earth/sciber/rocks2.htm
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Basalt
http//physics.uwstout.edu/geo/gallery/Dark_basalt
_lava.jpg
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Igneous rock forming intrusive or extrusive?
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Basalt erupted through reef intrusive or
extrusive?
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Texture of Igneous Rocks

• Glassy
• Similar to ordinary glass
• No visible crystals
• Pyroclastic
• Broken, angular fragments of rock material
• Explosive source

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Obsidian
http//physics.uwstout.edu/geo/gallery/obsidian.jp
g
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Explosive deposit - pyroclast
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Keys to Identification

• Start with texture!
• Identify mineral components
• Estimate percentage for each component
• Important to distinguish between quartz and
  feldspar

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What is my favorite rock?
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Olivine coated with basalt
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Green sand beach why green?
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Olivine!
http//www.biosbcc.net/ocean/marinesci/02ocean/hwg
eo.htm
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What is the main difference between volcanoes on
Earth and volcanoes on Mars?
SIZE!
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http//www.athena.cornell.edu/kids/cs_cabrol_quest
ions.html
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http//mars.jpl.nasa.gov/mep/science/oly-az.jpg
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http//volcano.und.nodak.edu/vwdocs/planet_volcano
/mars/Shields/size.html
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http//mars.jpl.nasa.gov/mep/science/3dom.jpg
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Martian Volcanoes

• Many are 10-100X bigger than any volcano on Earth
• Two main reasons
• Less gravitational pull volcanoes can grow
  bigger before collapsing under own weight
• Hot spots and crust stationary

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Volcanoes on Mars
http//www.athena.cornell.edu/kids/cs_cabrol_quest
ions.html
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Volcanoes on Mars
http//volcano.und.nodak.edu/vwdocs/planet_volcano
/mars/Overview.html
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Cinder Cones on Mars

• Probably mark sites of small explosive eruptions
• Similar to shield volcanoes on Earth probably
  still mostly basaltic lava

http//volcano.und.nodak.edu/vwdocs/planet_volcano
/mars/Other/cyd.html
http//volcano.und.nodak.edu/vwdocs/planet_volcano
/mars/Cones/Overview.html
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Cinder cones on Mars

• Steeper features generally older
• Change in nature of volcanism?

http//www.solarviews.com/eng/marsvolc.htm