On what basis are rocks classified?

Rocks are classified primarily based on their origin, which refers to the processes by which they are formed. There are three main types of rocks: igneous, sedimentary, and metamorphic.

Igneous rocks form from the cooling and solidification of molten material, known as magma or lava. Sedimentary rocks originate through the accumulation and compaction of mineral and organic particles, often occurring in layers over time. Metamorphic rocks arise from the transformation of existing rock types under conditions of high pressure and temperature, which can alter their mineral composition and structure.

While color, texture, and density can provide useful information about rocks and can sometimes aid in identification, they do not fundamentally determine the classification of rocks. The classification by origin provides a clear framework for understanding the geological processes that lead to rock formation, which is essential for studying Earth's geology and the rock cycle.