How do rocks form

The rock cycle is a concept used to explain how the three basic rock types are related and how Earth processes, over geologic time, change a rock from one type into another. Plate tectonic activity, along with weathering and erosional processes, are responsible for the continued recycling of rocks. The rocks in display are meant to be viewed in a clockwise direction.

As you walk, keep in mind that existing rocks may change through natural processes over geologic time, or event melt to form new rocks.

Sedimentary Rocks Sedimentary rocks are formed from pieces of other existing rock or organic material. There are three different types of sedimentary rocks: clastic, organic biological , and chemical. Clastic sedimentary rocks, like sandstone, form from clasts, or pieces of other rock. Organic sedimentary rocks, like coal, form from hard, biological materials like plants, shells, and bones that are compressed into rock.

The formation of clastic and organic rocks begins with the weathering , or breaking down, of the exposed rock into small fragments. Through the process of erosion , these fragments are removed from their source and transported by wind, water, ice, or biological activity to a new location. Once the sediment settles somewhere, and enough of it collects, the lowest layers become compacted so tightly that they form solid rock. Chemical sedimentary rocks, like limestone, halite, and flint, form from chemical precipitation.

A chemical precipitate is a chemical compound—for instance, calcium carbonate, salt, and silica—that forms when the solution it is dissolved in, usually water, evaporates and leaves the compound behind. These dissolved minerals are precipitated when the water evaporates.

Metamorphic Rocks Metamorphic rocks are rocks that have been changed from their original form by immense heat or pressure. Metamorphic rocks have two classes: foliated and nonfoliated. When a rock with flat or elongated minerals is put under immense pressure, the minerals line up in layers, creating foliation. Foliation is the aligning of elongated or platy minerals, like hornblende or mica, perpendicular to the direction of pressure that is applied.

An example of this transformation can be seen with granite, an igneous rock. Granite contains long and platy minerals that are not initially aligned, but when enough pressure is added, those minerals shift to all point in the same direction while getting squeezed into flat sheets. Nonfoliated rocks are formed the same way, but they do not contain the minerals that tend to line up under pressure and thus do not have the layered appearance of foliated rocks.

Sedimentary rocks like bituminous coal, limestone, and sandstone, given enough heat and pressure, can turn into nonfoliated metamorphic rocks like anthracite coal, marble, and quartzite. Nonfoliated rocks can also form by metamorphism, which happens when magma comes in contact with the surrounding rock. Igneous Rocks Igneous rocks derived from the Latin word for fire are formed when molten hot material cools and solidifies.

Igneous rocks can also be made a couple of different ways. When they are formed inside of the earth, they are called intrusive, or plutonic, igneous rocks. The Moon and our local planets — Mars, Venus and Mercury — are just the largest rocks floating around our part of space.

These are all made from space dust stuck together over billions of years. Planet Earth is a rock too, but so much has happened since it was formed from dust and small rocks that smashed and stuck together 4. As the space dust hit each other to make the earth, it got super hot and melted. The Earth was, at that time, a spinning ball of red-hot lava flying through space.

In this melted lava planet, heavy bits of the earth sank and the light frothy bits gathered on the surface. Have you ever looked closely at a glass of milky coffee at a cafe? The dark heavy coffee is at the bottom, whereas the light, frothy milk sits on the top. Well, our planet was a bit like that coffee billions of years ago. The rocks we see on the surface are like the frothy milk!

They were light and rose to the top. Then, as time moved on, the planet cooled and froze to become the solid earth we have now. I know most rocks are heavy. But in fact some rocks — even really big ones like Uluru — are actually much lighter than the rocks found in the deep Earth.

Volcanic lava in Etra Ale Volcano in Ethiopia in