Guide to Diamonds, Rocks, and Minerals

Studying rocks and minerals can help you learn about Earth. A rock is made from two or more minerals. A mineral might contain just one chemical element or more than one element. Scientists guess that the Earth contains about 4,000 different minerals. The diamond is the Earth’s hardest mineral. A diamond is so hard that it’s possible to cut a diamond with another diamond.


Rocks divide into three different groups according to how they are formed. The three different rock types are sedimentary, igneous, and metamorphic. Sedimentary rocks often develop in water as layers of sediment build up over time. Sedimentary rocks include sandstone, flint, and chalk. Igneous rocks are created when magma cools and then hardens. Igneous rocks include basalt, granite, obsidian, and pumice. Metamorphic rocks have this special name because they change from pressure and heat. Types of metamorphic rocks include marble, granulite, quartzite, and slate.

Rocks can give people excellent clues about the history of Earth. Rocks are records that can tell scientists important information about what Earth looked like and what the atmosphere was like long ago. When scientists understand Earth’s history, they can better understand why and how the planet is the way it is today. Scientists can also try to predict what might happen to Earth in the future. Rocks form under certain conditions, so when scientists find specific rocks in certain places, they can guess about environmental conditions that had to be present for the rocks to be where they were found.



Geologists have a special definition of minerals. To be called a mineral, a substance has to fit five different scientific rules. Minerals occur naturally, and they are inorganic. Naturally occurring objects are things that people have not made. Inorganic objects are things that organisms have not made. For example, wood is natural, but it comes from trees. This means that wood is not a mineral. Minerals have a definite chemical composition, and they are a solid substance. A definite chemical composition means that all occurrences of a mineral have a content that will only change within a limited range. Solid substances are not a gas or a liquid when at typical temperatures and pressure. Finally, minerals have an ordered internal structure. This means that the atoms contained in a mineral are arranged in a specific and repeating pattern. The things you see and touch around you are made up of a combination of minerals. People use a huge number of minerals in their everyday lives. Scientists estimate that people in the United States use about three trillion tons of minerals every year. This is about 10 tons of minerals every year for every American citizen.



Diamonds, the strongest minerals on Earth, are located deep under the Earth’s surface. Diamond formation needs four specific things to happen. Carbon has to be present, and then pressure and heat have to happen to the carbon over time. The heat has to be at least 752 degrees Fahrenheit, and the pressure has to be at least 434,113 pounds per square inch. The best depth for diamond creation is about 100 miles beneath the Earth’s mantle. At some point, volcanic eruptions moved diamonds at these extreme depths up so they were easier to find. If you were to find a diamond in the dirt, it would not look bright and shiny. It’s only after cutting and polishing that diamonds look brilliant and sparkling.


"It's the best thing I ever bought for myself. I wear my jewelry now. I'm just sad I missed out all these years, but there's no going back I am so glad I finally did this!"

- Patrice in LA