Igneous Rock Key


Crystal Size Composition Rock
Phaneritic Ultramafic Peridotite
Mafic Gabbro
Intermediate Diorite
Felsic Granite

 
Crystal Size Composition Rock
Aphanitic Mafic Basalt
Intermediate Andesite
Felsic Rhyolite

 
Crystal Size Composition Rock
Porphyritic Mafic Basalt Porphyry
Intermediate Andesite Porphyry
Felsic Rhyolite Porphyry

 
Texture Color Rock
Glassy Black, brown, red Obsidian
Vesicular
(containing a great number of bubble holes formed by escaping gas)
Dark; heavy Vesicular Basalt
Dark; light weight Scoria
Light Pumice
Pyroclastic
(ash and broken pieces of lava and glass formed into rock)
Any color Tuff or Breccia