All rocks can be separated into three families. What are they?

All the rocks on Earth are categorized based on how they were formed. The first type originates from molten rock, or magma, deep within the planet. When this magma cools and solidifies, it creates igneous rocks. Some, like granite, cool slowly underground, developing large, visible crystals. Others are formed from lava that erupts onto the surface, cooling quickly and creating rocks with fine-grained or even glassy textures, such as obsidian and basalt.

The second family of rocks is created by the accumulation of sand, silt, and the remains of dead plants and animals. Over long periods, layers of this debris are deposited, often at the bottom of lakes and oceans, and the weight from above compacts them together to form sedimentary rocks like sandstone and shale. Because of how they are formed, these rocks often have visible layers and are the most common type to contain fossils.

Any existing rock can be transformed into a third type by being subjected to intense heat and pressure deep within the Earth's crust. This process, which does not melt the rock but fundamentally changes its structure, creates a metamorphic rock. For example, limestone, a sedimentary rock, will transform into marble, while granite, an igneous rock, can become gneiss. These three distinct formation processes give us the main families of rocks, all interconnected through a constant process of creation and transformation known as the rock cycle.