The correct answer is - a) by their texture.
Rocks are being mainly classified by their composition and their texture. Their texture represents the structure of the rocks. The three types of rocks igneous, sedimentary, and metamorphic have different texture classifications. Their textures depend on the place of their formation, the temperature, the pressure etc.
- Igneous rocks according to their texture are divided into:
* Intrusive rocks
* Extrusive rocks
- Metamorphic rocks are divided into:
* Quartizite
* Schist
* Gneiss
* Slate
* Phyllite
- The sedimentary rocks are divided into:
* Clastic
* Chemical
* Biochemical