Scientist classify rocks into three different ways . what is the main basis for the classification system they chose

The three main types of rocks are:

1. Igneous rock
2. Sedimentary rock
3. Metamorphic rock

They are classsified by their formation :

Igneous rock- This type of rock is formed due to volcanic activities, and under this type of rock, it is seperated into volcanic rock and plutonic rock.

Volcanic rock is also called intrusive igneous rock, where the magma filled the cracks below surface and cools down without meeting the air. One of the example if this kind of rock is granite.

Plutonic rock is also known as extrusive igneous rock where volcanic eruption occurs and the lava cools down after being exposed to the air. One of the example is tuff.

Sedimentary rock- These kind of rocks are formed due to the accumulation of sediments overtime. Rocks are also divided into two types under this catagory, namely clastic and non-clastic sedimentary rock.

Cladtic sedimentary rock - It is where the particles of sediments gets compacted due to accumulation, and the rock is usually coarse grained with different size of particles, for example, breccia.

Non-clastic on the other hand, are formed by organic substance that existed for a very long time to become rock, for example, coal is a kind of rock that is formed by organic substances under million years of accumulation. It is posible that fossil will be found.

Metamorphic rock- These type of rocks under goes extreme high temperature or compaction to form a new kind of rock from their parent rock. For instance, igneous rock will turn into marble under high temperature.

Hope it helps!

What exactly do you mean 

Answer decreased soil salinity;