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
Course
Crystal size
1mm to 10mm
Very Course
Crystal size
10mm or larger
Fine Texture
Fine
Crystal size
Less then 1 mm
Glassy Texture
Crystal size
Non-crystalline
Meaning no visible crystals
Vesicular Texture
Visible gas pockets
Mafic Intrusive rock
Gabbro
Large crystals
Dark in color
Mafic extrusive rock
Basalt
small crystals
Dark in color
Felsic Intrusive rock
Granite
Large crystals
Light in color
Felsic extrusive rock
Rhyolite
Small crystals
Light in color