Identification of Igneous Rock

You have identified either porhorytic andesite or porphoytic diorite.
In order to ditinguish between the two take a closer look at the matrix. If the porphorytic texture can be descibed as large crystals in a phaneritic matrix then you have identified porphorytic Diorite. If, on the other hand, the porphorytic texture can be descibed as large crystals in an aphanitic matrix you have identified porphorytic andesite.

Texture

Felsic

Intermediate

Mafic

Ultramafic

Pegmatitic

Granite-pegmatite

Diorite-pegmatite

Gabbro-pegmatite

Phaneritic

Granite

Diorite

Gabbro

Rarely seen

(Komatiite)

Aphanitic

Rhyolite

Andesite

Basalt

Porphyritic

Porphyritic Rhyolite
or
Porphyritic Granite

Porphyritic Andesite
or
Porphyritic Diorite

 

Glassy

Obsidian

Vesicular

Pumice

Scoria

Pyroclastic

Tuff

 

 

©2006 Sean Tvelia