Igneous Rocks Notes

Intrusive Igneous Rock

• Large - 1 mm or greater in size. Visible.
• T.I.R.A.C - Tightly Interlocking Randomly Arranged Rocks
• Formed from molten rock material
• Inside the Earth (INtrusive)

Extrusive Igneous Rock

• T.I.R.A.C. - Harder to see because the crystals are too small to see. Appear chalky.
• Size - 1 mm or smaller to non existent (glass)
• Glassy- shiny
• Vesicular- Gassy, bubbly, foamy.
• They formed from molten rock material.
• On the outside of Earth, (EXterior, EXtrusive)

Felsic Igneous Rocks

• General - Pink, white, yellow.
• Quartz- varied, usually clear to grey
  Potassium Feldspar - Pink, White or Yellow.
  Others tend to be black to blackish/green
• Potassium Feldspar (Orthoclase)

  Quartz
• Amphibole

  Biotite

  Plagioclase Feldspar (dirty gray)

Mafic Igneous Rocks

• General - Dark, which makes it difficult to see T.I.R.A.C.
• All the minerals are Black/Black Green.
• Often have rust stains, that do not penetrate the rock.
• Olivine
  Pyroxene
• Amphibole

  Biotite

  Plagioclase Feldspar (dirty gray)