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What is a Mineral?

What is a Mineral?

The year is 1850. You have packed up everything you own and traveled west to California to join in the Gold Rush. You have heard of people striking it rich and have come to stake your claim. Then, one afternoon you come across the mineral nugget shown in the image. You've done it, you've found gold! Or have you?

What you have found is a mineral, just not the mineral you were looking for. A mineral is a naturally occurring, crystalline solid, with a definite chemical composition that forms by inorganic processes. Let's break that definition down:

  • Naturally Occurring - A mineral must form by natural processes. Synthetic gemstones can be created in laboratories. These are technically not considered minerals because they did not form in nature.

  • Crystalline Solid - Minerals must be solid, not a liquid or gas. They also must be crystals. The atoms in a crystal arrange in a geometric pattern. This is what gives minerals their distinct shapes.

  • Definite Chemical Composition - Minerals are made of elements. Some minerals like gold may contain only one element. These are called native elements. Most minerals are made of more than one element. Each type of mineral will have the same combination of elements in the same proportions. Some minerals will have small amounts of additional elements, called impurities. Impurities can cause one type of mineral to come in several different colors. Minerals are classified into groups based on their chemical compositions.

  • Formed by Inorganic Processes - Minerals are not living. They are not made from parts of organisms. They must be able to form inorganically. Some minerals may be formed by inorganic processes produced by organisms.

Minerals are identified by their properties. Major mineral properties include color, streak, hardness, luster, specific gravity, cleavage, fracture, and crystal form. These properties are useful when geologists identify minerals in the field. However, laboratory analysis with X-ray diffraction provides definitive mineral identification. Minerals are the building-blocks of rocks. A rock may consist of only one mineral. It may have many different minerals.

The mineral you found is pyrite, also known as fool's gold. It has the same metallic luster and a similar color as gold. It can sometimes occur in nature along with gold. But that is where their similarities end. Pyrite contains mainly the elements iron and sulfur. Gold is a native element. Pyrite forms distinct cubic crystals seen in the image. It tends to break while gold tends to bend. Compared to gold, pyrite is a much harder mineral. Looks like you need to keep panning for gold. Better luck next time!


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