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Texture Of Igneous Rocks

Texture- 
                  The texture of a rock is the size, shape, and arrangement of the grains (for sedimentary rocks) or crystals (for igneous and metamorphic rocks). 

It is basically divided into 4 parts:
1. Crystallinity (Degree of Crystallization)
2. Granularity (Actual Size Of Grain)
3. Shapes Of Crystals
4. Mutual Arrangement Of Grain

1. Crystallinity- Ratio between Crystallised and Non Crystallised materials.

a) Holocrystalline- Rock composed entirely of crystal.
b) Hemicrystalline- Rock composed of crystal and glass.
c) Holohyalline- Rock composed entirely of glass.

2. Granularity- Actual size of grain.

a) Phaneritic/Phanerocrystalline- When we can identify the crystals by naked eye, formed during plutonic environment.
 Coarse Grained- >5 mm
 Medium Grained- 1 to 5 mm
 Fine Grained- <1 mm

b) Aphanetic- When we can't identify crystals by naked eye.
 Microcrystalline- Rocks that contains small crystals, visible only through microscope.
 Cryptocrystalline- When crystals are too small to be distinguished,even under the microscope.

3. Crystal Shape- 

 Euhedral- Crystal boundary is perfect grown.
 Subhedral- Crystal boundary is partially develop.
 Anhedral- Crystal have no boundary.
 Tabular- Crystal grain grow in 2 opposite direction and 3rd dimension remain undeveloped.
 Prismatic- Crystal outline is developed in one direction compare to other direction.
 Equidimension- Crystals are equally developed in all directions.

4. Mutual Arrangement Of Grain- 

a) Non-Directive- Grain do not show parallel orientation or arrangement of grain.

(1) Equi-granular- Minerals are even grained in hand specimen.
  Panidiomorphic- Majority of crystals are euhedral.
  Hypidiomorphic- Majority of crystals are subhedral.
  Allotriomorphic- Majority of crystals are anhedral.

(2) Inequigranular- When grain size are not equal.
 Porphyritic- Large crystals are enclosed by small ones.
 Large crystals are called Phenocryst and small are called groundmass or matrix.
 Poikilitic- Small crystals are enclosed by large ones.









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