3. a. Leucocrative; this type of rocks have light
color .
b. Mesocrative; this type of rocks occur in
medium dark colur.
c. Melamocrative; this type of rocks ocour in dark
colour.
9/30/2015 3
7. The size of grains in an igneous rock varies
considerable. The slow cooling gives crystals
time to grow to size greater than 5mm.In
rapid cooling, the mineral grains crystallize
quickly as a mass of tiny crystals which are
generally less than 1mm in size. In some
laves, the is so rapid that they fail to
crystallize and “glassy texture”results.
9/30/2015 7
8. 3. Shap of the crystal; the grains of an
igneous rock are called “euhedral” if
they show developed crystal faces,
and if the crystal faces are partly
developed, they are described as
“subhedral”.
9/30/2015 8
9. 4. Mutual relations of grains ;
They are following types;
A. Equigranular
a.panidiomorphic texture; when most
of the grains are euhedra.ex-
lamprophyres.
b.Hypidiomorphic texture; hen most of
the crystals are subhedral.ex-granite
and syenites.
9/30/2015 9
10. e. Orthophyric texture; some highly
rocks such as orthophyres and
plagiophyers.
f. felsitic texture; An igneous rocks
containing a uniform mass of
cryptocrystalline matter. 9/30/2015 10
12. d. Intergranular and instersertal texture ;in
many basalts plagioclase laths occur in such
away that they form a network with triangular
or polygonal interspaces.
9/30/2015 12
19. Extrusive; extrusive
igneous rock
bodies are formed
from magma
poured out at the
surface. ex-
lavaflows
Instrusive; these
types of bodies are
formed by the
consolidation of
magma at some
depth below the
earth surface. Ex-
batholith
9/30/2015 19
24. Nature
Texture
a. Grain size
b. Roundness
c. Sorting
d. Packing
structures
9/30/2015 24
25. Clastic sediments; clastic rocks are formed by
the mechanical accumulation of grains of
clastic sediments.
Depending upon the size of constituent
grains they are following types-
Rudaceous rocks; these rocks are formed by
accumulation of bigger rocks fragments such
as gravels, pebbles and boulders.
Arenaceous rocks ; these rocks are composed
almost entirely of and grains . Ex -sandstone
Argillaceous rocks; these rocks are made up
of very fine grained sediments. Ex-shale
9/30/2015 25
32. Stratification ; all the sedimentary rocks are,
in general, characterized by “stratification”.
deposition of sediments into layers or beds is
called stratification.
Lamination ;the bedding, less than one
centimeter in thickness, are called
“lamination”.
9/30/2015 32
36. a. Leucocrative; this type of rocks have light
colour .
b. Mesocrative; this type of rocks occur in
medium dark colour.
c. Melamocrative; this type of rocks occour in
dark colour.
9/30/2015 36
37. Crystalloblastic texture; the holocrystalline
texture of metamorphic rocks is called the
“crysalloblastic texture” .this type of of
texture develop s due to recrystallisation of
minerals grains in the solid medium.the
crystals showing perfect crystal outline, are
called the “idioblastic” while those which do
not have any definite shape, are described as
“xenoblastic”.
9/30/2015 37
38. Granoblastic texture; in a metamorphic rock if
the major constituents are granular or
equidimensional, the texture is called
“granoblastic”.
Palimpest texture; the remnant texture of the
parents rock found preserved in the metamorphic
rock, is called “palimpest texture”.
9/30/2015 38
40. Cataclastic structure;
These rocks are formed mainly under the
influence of shearing stresses in the upper
zones of the earth’s crust.
Maculose structure; when argillaceous
rocks are subjected to contact
metamorphism, a spotted rock is formed in
areas where incomplete recrystalization
takes place.
9/30/2015 40
41. Schistose structure ; the foliation of schists is
called “schistosity”.
Gneissoses structure; such a coarse grained
metamorphic rocks showing baned or
streaked appearance, is called “gneiss”and its
structure is called the “gneissose structure”.
9/30/2015 41
42. Hornfelsic structure; this type of rocks is
formed due to the predominance of
equidimentional minerals such as felspar,
andalusite, cordierite, and quartz.
9/30/2015 42
