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Highly cllasification of the igneous rokcs
Typology: Exercises
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SUPERVISED BY
SUBMITTED BY
DR.S.C.MATHUR
RAMESH KUMAR
M.Sc
II Sem
Igneous textures
Glassy
texture
Glassy Obsidian
(I) Phaneritic
(coarse-
grained)
texture
Slow cooling
Crystals can
be identified
without a
microscope
(1) Equigranular:- Basis of eqiual size:-
(a) panidiomorphic:- when grains are euhedral.
Ex. - Lamprophyres
(b) Hypidiomorphic :- crystals are subhedral. Ex.-
syenites
(C) Allotriomorphic:- crystals are anhedral. Ex. –
aplites
(d) Microgranular:- it is equigranular which
unhedral and subhedral
orthophyres and plagiophyres possess a fine
grained panidiomorphic texture.
mass of cryptocrystalline matter.
(c) Ophitic:- Bigger crystals of augite
enclose smaller laths of plagioclase. If the
plagioclase laths are only partly enclose in the
larger grains of augite, is sub-ophitic.
Ex. Dolerite
(d) Intergranular and instersertal:- In many
basalts plagioclase laths occur in such a way that
they form a network with triangular or polygonal
interspaces.
These interspaces are filled with minute grains of
augite, olivine and iron oxide. It is texture of
intergranular. When glassy or fine grained
chloritic or serpentineous material occur in the
interspaces is intersertal.
(3) Directive Texture:- Result of flow of magma during the formation of rocks. These exhibit
perfect or semi-perfect parallalism of crystals or crystallites in the direction of the flow of
magma.
(a) Trachytic:- Certain volcanics rocks such as trachyte, contain feldspar laths arranged in lines
parallel to the direction of flow of lava.
(d) Hyalopilitic:- In a volcanic rocks if feldspar laths are found intermixed with glass.
(4) Intergrowth Texture:- More minerals may crystallize out simultaneously in a limited space.
Ex. Graphic and granophyric texture.
