Lab 5 igneous rocks
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Lab 5 – Igneous Rocks. Volcanic hazards Tungurahua, near Banos, Ecuador. Igneous rocks. Igneous rocks – formed from cooled molten rock Intrusive (magma) – coarse grained Extrusive (lava) – fine grained Two stages – fine grained matrix with larger crystals (phenocrysts).

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Lab 5 – Igneous Rocks

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Lab 5 igneous rocks

Lab 5 – Igneous Rocks


Lab 5 igneous rocks

Volcanic hazards Tungurahua, near Banos, Ecuador


Igneous rocks

Igneous rocks

  • Igneous rocks – formed from cooled molten rock

  • Intrusive (magma) – coarse grained

  • Extrusive (lava) – fine grained

  • Two stages – fine grained matrix with larger crystals (phenocrysts)


Igneous textures

Igneous Textures

  • Glassy texture – very rapid cooling of viscous lava  volcanic glass

  • Aphanitic texture – rapid cooling, ign. rocks with crystals too small to see (fine grained)

  • Phaneritic texture – slow cooling, ign. rocks with crystals that are visible (coarse grained 1-10mm)


Igneous textures1

Igneous Textures

  • Pegmatitic texture – last to cool, very course grained crystals (>1cm)

  • Porphyritic texture – represents two periods of cooling, composed of large crystals (phenocrysts) in a fine grained matrix

  • Vesicular texture – ign. rocks with vesicles in them  cause by gas bubbles being trapped in the cooling lava.


Lab 5 igneous rocks

Aphanitic

Phaneritic

Glassy

Porphyritic

Vesicular

Pegmatitic


Felsic v mafic

Felsic v. Mafic

  • Felsic

    • Quartz, plagioclase feldspar, K-spar, and muscovite

    • Light in color (generally)

  • Mafic

    • Biotite, amphibole, pyroxene, and olivine

    • Dark in color (generally)


Igneous rock classification

Igneous Rock Classification


How to identify

How to Identify

  • Identify color (light/dark), but be careful!

  • Identify the minerals in the rock (if it’s not too fine grained)

  • Identify textures

  • Classify the rock using the flow chart in Fig. 5.2 and Fig. 5.3


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