TEXTURE OR STRUCTURE OF A ROCK

The arrangement of minerals forming a rock is known as its texture or structure o. Following are the different types of textures:

1. Compact Crystalline- The fine grains or particles are held together in a compact crystalline form e.g. marble, quartzite, etc.
2. Conglomerate- The grains are round and of different sizes. They are cemented by some binding material.
3. Foliated- In this types of texture the arrangement of minerals is in the form of parallel layer.
4. Glassy- It is like glass without any crystal.
5. Granular Crystalline- The crystals are of similar size. They are separate, But they are held together by some binding materials e.g. sandstone, gneiss etc.
6. Pisolitic- The grains are bigger in size and they are as large as peas.
7. Porous Granular- The grains are in the form of irregular minute particles and a rock with such texture is not durable.
8. Porphyritic- In this type of texture the crystals of one or more of minerals are large and predominant.
9. Vesicular- This texture is indicated by small irregular cavities on rock surface.
10. Pyroclastic- A pyroclastic texture shows a mixture of rock fragments, pumice and volcanic ash. The ash is very fine grained so only the rock fragments and pumice are identifiable. A rock with pyroclastic texture is termed as tuff if the largest fragment are then 2.5 inches long, a volcanic breccia if the fragments are larger.