Rocks are classified according to the major Earth processes that formed them. They are generally classified by mineral and chemical composition, by the texture of the particles that formed them and also depending on the rock cycle.

There are three types of rocks: Igenous, Metamorphic, and sedimentary.

Igenous rocks: Are melted rocks that cooled and solidified, when melted magma cools.  They are divided in two main categories:  

• Plutonic: When magma cools down and crystallizes, like the granite, and 
• Volcanic: When magma reaches the surface as lava or fragment, like pumice, granite and basalt.

Metamorphic rocks are compacted by pressure and heat from deep inside the earth.  They are formed by subjecting any rock type to different temperatures and pressure conditions than those in which the original rock was formed. 

Marble is a Metamorphic rock with a parent rock of limestone or dolostone and is formed by natural processes of heat and pressure. some other metamorphic rocks are quartzite, slate, schist, gneiss

Sedimentary rocks are formed at the surface of the earth. They are formed  by deposition of either clastic sediment, organic matter or chemical precipitates because of the high pressure and temperature.  They are formed in water or on land.  They are layered accumulations of sediments, fragments of rocks, minerals or animal or plant material. 

Some Sedimentary rocks are limestone or limestone karst formations which we can find in caves e.g Sandstone, gravel

These rocks are distributed all across the mountains, valleys, and plains, in river beds, in mines and on beaches (pebbles and sand)