-
reflects differences
in mineral crystal size.
Texture
-
Large crystals easily
seen, course –grained.
Phaneritic
-
Very tiny crystals,
individual crystals cannot be seen without magnification, fine-grained.
Aphanitic
-
igneous rock with
mixed texture with both large and small grained crystals.
Porphyry
-
large crystals in a
porphyry
Phenocrysts
-
existing
rock in the countryside prior to intrusion by magma
Intrusive
igneous rock – has forced its way into the surrounding country rock.
Country rock
-
magma which has come
to the surface and cooled more rapidly, come from volcanoes
-
magma which flows out
on the surface of the earth.
Pyroclastic rocks
-
very tiny droplets of
magma thrown into the air, often glass.
volcanic ash
-
larger pieces of
volcanic rocks thrown into the air, cooled and formed as they fall.
Bombs
-
name for all pyroclastic
rocks (those thrown into the air)
Tuff
-
volcanic glass filled
with air pockets called vesicles.
Pumice
-
from lava flows, very
tiny vesicles, very solid and dense. Comprised entirely of glass.
Obsidian
-
a liquid’s resistance
to flow. Resistance increases with an increase of silica. Mafic rocks have low
viscosity, felsic rocks have a high viscocity.
Viscosity
|
|
