Igneous rocks

Igneous rocks

1. Extrusive

2. Intrusive

   • An intrusive rock is formed underneath Earth's surface, from magma which cuts across existing rock.
   • There are 2 main types of intrusion.
     • Major intrusion (plutonic)
       • Usually a batholith
     • Minor intrusion (hypabyssal)
       • Dyke
         • A dyke is a sheet-like intrusion, which is often vertical and discordant.
           • Can be a few centimetres thick or >100km thick.
       • Sill
         • Transgressive sill
           • A sill that cuts across beds in steps from one to another.
         • A sill is a sheet-like intrusion, which are often concordant and parallel to country rock (any rock an igneous rock is intruded into).

3. A chart to identify igneous rocks

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