Igneous rocks are classified by
mineral composition and texture
What are the six different textures of igneous rock
Aphanitic, phaneritic, porphyritic, glassy, pyroclastic and vesicular
In laymans terms what does aphanitic mean?
Fine grained less than 1mm
In laymans terms what does phaneritic mean?
Visible with naked eye, coarse grained
Porphyritic means
two different grain sizes apparent in the rock
Porphyritic with phaneritic groundmass resembles a
chocolate chip oatmeal cookie
Porphyritic with aphanitic groundmass resembles a
peanut butter cookie
What is the only rock you need to know that has pyroclastic texture?
lapilli tuff
vesicular texture is formed when lava solidifies before gases are able to escape, the result is a
bubbly appearance
What are the felsic (light minerals) minerals?
Quartz, k-feldspar, muscovite and plagioclase (labradorite and albite)
What are light minerals called?
Felsic
Mafic or dark minerals are
Biotite, hornblende, pyroxene, olivine
Dark minerals are called
Mafic
What are diagnostic properties of biotite?
Black, shiny excellent planar cleavage
What are diagnostic properties of hornblende
Black, shiny, long with two cleavages at 60 and 120 degrees
Diagnostic properties of pyroxene?
Dark green, dull, stubby, 2 cleavages at 90 degrees
Diagnostic properties of olivine?
green, glassy, "sugary
Diagnostic properties of quartz
Clear, light greyish, conchoidal fracture
Diagnostic properties of k-feldspar?
often pink
Diagnostic properties of muscovite?
Colorless, shiny
Diagnostis properties of plagioclase
White to dark, striations
Texture of granite with 5% mafics?
Porphyritic with phaneritic groundmass
Mafics of less spotted granite
5%
Composition of granite?
felsic
Minerals found in granite?
K-feldspar, quartz, plagioclase, biotite
Mafics of granite with phaneritic texture?
20%
Texture of granite with 20% mafics?
phaneritic