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What is texture? What is the importance of study of texture? On the basis of which factors the textures of sedimentary rocks are divided?

 Texture: The term texture represents the shape, size, and mutual arrangement of mineral grains in a rock. The texture of sedimentary rocks includes grain size, shape (Sphericity and roundness), fabric, packing, etc.

The importance of the study of texture are-

a)      To determine the useful physical properties such as porosity, permeability, and crushing strength.

b)      To find out the dispersion pattern by textural measurements.

c)      To make the distinction among the Stratigraphy unit.

1)      Grain size: On the basis of grain size, the texture of sedimentary rocks can be divided into the following groups-

·         Pebble: If the grains size is more than 10 mm then it is called pebble.

·         Gravel: If the grains size is between 2mm to 10 mm then it is called gravel.

·         Sand: If the grains size is between 0.1 mm to 2 mm then it is called sand.

·         Silt: If the grains size is between 0.01 to 0.1 mm then it is called silt.

·         Clay: If the grains size less than 0.01 then it is called clay. 

2)      Shape: In geometry, a shape can be defined as the form of an object or its outline, outer boundary, or outer surface. The shape of sedimentary particles can be defined in many ways. But there is a simple way to classify the shape of sedimentary particles, which was introduced by Zingg in 1935. He used a ratio …..

On the basis of these ratios, four shapes are identified-

a)      Tabular

b)      Equant

c)      Bladed

d)      Prolate

 

3)      Roundness: Roundness refers to the curvature of the corners of the grains. They are divided into the following categories-

a)      Angular.

b)      Very angular.

c)      Sub-angular.

d)      Rounded.

e)      Sub-rounded.

f)       Well rounded.  

4)      Sorting: Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. Shorting is of types-

a)      Very poorly sorted

b)      Poorly sorted

c)       Moderately sorted

d)      Well sorted

e)      Very well sorted

5)      Sediment fabric: Fabric refers to the mutual arrangement of grains in sediments. It includes the orientation of grains and their packing. Sedimentary rock may contain elongated particles; their orientation is described in terms of their long axis.  If all or most of the elongated particles are arranged in such a way that the longer axis lies in the same direction then the rock is said to show a high degree of preferred orientation.

Packing refers to the arrangement of clastic grains and Intergranular space in between them.  

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