Skip to main content

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.









Comments

Post a Comment

Popular posts from this blog

CIPW NORMS CALCULATIONS

CIPW NORMS CALCULATIONS The CIPW norm is named after the four petrologists, Cross, Iddings, Pirsson and Washington, who devised it in 1931. What is a Norm and why it is needed? A norm is a means of converting the chemical composition of an igneous rock to an ideal mineral composition. It often reveals similarities in rocks that have quite different modes, or observed mineral assemblages. Some of the factors that can cause such variations are: • Disequilibrium (for example, zoned minerals or reaction rims isolating the interiors of grains) • Temperature • Pressure • Alteration • Water content (otherwise identical rocks might contain biotite, amphibole, or pyroxene, depending on water content) • Other minor constituents. For example, excess sulfur or chlorine might cause scapolite to form instead of feldspar. Boron typically causes tourmaline to form. The CIPW norm calculates mineral composition as if the magma were anhydrous (water is simply treated as a separate phase) and at low press...
Post a Comment
Read more

Branches Of Geology

1. Mineralogy-                       Mineralogy defined as the offshoot of geology dealing with the scientific analysis of the minerals, including chemistry, structure, physical and optical properties and its artifacts. 2. Structural Geology-                                   The   branch of geology dealing with the three-dimensional distribution of the rock and its deformational history.  3. Oceanography-                             The discipline of geology dealing with the studies of oceans and seas including their framework, physical and chemical properties, origin and its ancient history and current direction.  4. Petrology-                     Petrology is systematic studies of rocks, their origin, structure, c...
Post a Comment
Read more

FOSSILISED LEAVES FROM JURASSIC PERIOD IN JHARKHAND

 Geologists Discover Fossilised Leaves From Jurassic Period in Jharkhand Geologists have found fossilised leaves, estimated to be around 150-200million years old, in Jharkhand's Sahibganj district. A couple of 20 cm by 5 cm fossilised leaves of genus Ptilophyllum have been found in Dudhkol mountain in Taljhari area on 26/09/2020 and further excavation is underway, lead geologist assistant professor Ranjit Kumar Singh of Sahibganj PG College said. The excavation is being conducted in association with National Botanical Research Institute, Lucknow under a project of the Department of Science and Technology of the Union government. "Such leaves were consumed by herbivorous dinosaurs. Smaller fossils from Upper Jurassic to Cretaceous period were earlier found in the region. We might even find fossilised dinosaur eggs during further excavation," Singh told .
Post a Comment
Read more