How does rock form

As a terrestrial planet, Earth is divided into layers based on their chemical and rheological properties. And whereas its interior region — the inner and outer core — are mostly made up of iron and nickel, the mantle and crust are largely composed of silicate rock. The crust and upper mantle are collectively known as the lithosphere, from which the tectonic plates are composed.

It in the lithosphere that rocks are formed and reformed. And depending on the type of rock, the process through which they are created varies. In all, there are three types of rocks: igneous, sedimentary, and metamorphic. Each type of rock has a different origin. Igneous rocks are formed when melted rock cools and solidifies.

Some examples of igneous rocks are granite, scoria, pumice, and obsidian. Typically, granite makes up large parts of all the continents. The seafloor is formed of a dark lava called basalt, the most common volcanic rock.

Basalt is also found in volcanic lava flows, such as those in Hawaii, Iceland, and large parts of the U. Granite rocks can be very old.

Some granite, in Australia, is believed to be more than four billion years old, although when rocks get that old, they've been altered enough by geological forces that it's hard to classify them.

Sedimentary rocks are formed from eroded fragments of other rocks or even from the remains of plants or animals. The fragments accumulate in low-lying areas—lakes, oceans, and deserts—and then are compressed back into rock by the weight of overlying materials.

Sandstone is formed from sand, mudstone from mud, and limestone from seashells, diatoms, or bonelike minerals precipitating out of calcium-rich water. Metamorphic rocks are sedimentary or igneous rocks that have been transformed by pressure, heat, or the intrusion of fluids.

The heat may come from nearby magma or hot water intruding via hot springs. It can also come from subduction, when tectonic forces draw rocks deep beneath the Earth's surface. Marble is metamorphosed limestone, quartzite is metamorphosed sandstone, and gneiss, another common metamorphic rock, sometimes begins as granite.

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Rocks are classified into three basic types based on how they are formed. Igneous - A rock formed by the cooling and crystallization of magma molten rock at or below the Earth's surface. Sedimentary - A rock formed as a result of the weathering process, either by compaction and cementation of rock mineral fragments, or the precipitation of dissolved minerals.