Theory:

The rocks are the naturally occurring solid materials or the agglomeration of minerals forming the earth’s crust or lithosphere. The word ‘lithosphere’ means the ‘sphere of rock’ or ‘rock sphere’.  The rocks are made up of single or more minerals.
A rock does not necessarily look like a hard, massive sized stone, at times it may be soft small textured particles like mud, clay, sand etc as well. A small unit of the rock is called an element.
 
The rocks based on the origin are categorized into three major types as - Igneous, Sedimentary and Metamorphic.
 
rock types.png
 
rocktype.png
Reference:
https://www.open.edu/openlearn/science-maths-technology/science/geology/rock-types