Igneous Rocks

Igneous rock definition

• Rocks formed by the cooling and solidifying of molten materials. Igneous rocks can form beneath the Earth’s surface from magma, these are intrusive igneous rocks

• Or on the earths surface from lava, these are extrusive igneous rocks

Igneous Rock characteristics

• Texture: Very Course, Course, Fine, Glassy, Vesicular and non-vesicular

• Color: Light or Dark• Density: High or Low• Composition: Felsic Al, Si or Mafic Fe, Mg

• If a Rock is Dark in color it will also have a Mafic composition and a High density.

• If a rock is Light in color it will also have a felsic compostion and a Low density

Very Course to Course Texture

Very CourseCrystal size

10mm or larger

CourseCrystal size

1mm to 10mm

Fine TextureFine

Crystal sizeLess then 1 mm

Glassy TextureCrystal size

Non-crystalline Meaning no visible crystals

Vesicular TextureVisible gas pockets

Mafic Intrusive rockGabbro

Large crystalsDark in color

Mafic extrusive rockBasalt

small crystalsDark in color

Felsic Intrusive rock Granite

Large crystalsLight in color

Felsic extrusive rockRhyolite

Small crystalsLight in color