Minerals
If you subtract away all the organic life on Earth (e.g., trees, plants, animals, bacteria, and fungus), you are only left with minerals within the Earth’s crust. These minerals make up everything from the oceanic and continental plates we just learned about in the last Module to the soil that grows our plants. They are economically important because everything from the components of your smart phone or tablet to the can of Coca Cola you’re drinking all had to come from minerals. Minerals are everywhere!
Before we get too far ahead of ourselves, you’ll have to think back to your high school (or college) chemistry course or take a look at a periodic table to re-familiarize yourself with the basic building blocks of the universe: atoms and how atoms are characterized into elements based on the number of protons each has.
(Read section 3.1 of your textbook, pp 74 – 79).
Okay, so that was a pretty short reading. Let’s recap a bit.
What is a mineral?
A mineral is an Earth substance with the following qualities:
- It must be naturally formed. In other words, people, animals, or plants could not have made it. It had to have been naturally formed from physical and chemical Earth processes. It cannot have been formed from biological processes.
- It must be found on the Earth’s crust as a solid. This means that it can’t be a liquid or gas. This means that mercury (in its native or pure elemental form), which is a liquid at normal Earth temperatures – it doesn’t become solid unless it’s < - 39 °C (or very high pressures) –, is technically a mineraloid. It can form a solid but not at normal Earth temperatures and pressures.
- It must have a characteristic chemical formula. This means that the chemical make-up up of the mineral must be the same whenever it is found. Take a look at the images on the right: Pyrite also known as fool’s gold, because it kind of looks like gold, is always found as FeS2 (iron disulfide); Quartz is always found as SiO2 (silicon dioxide); and Kimberlite also known as diamond is always found as C (pure crystalized carbon).
- It must have a characteristic (distinct) crystalline structure. This is very important – and is why being a solid at Earth temperatures and pressures isn’t always enough. Every mineral must form into the shape of a crystal which is determined by the shape of the chemical bonds holding together the atoms of the mineral. This means that molecules with a distinct chemical formula will always form into the same distinctive shape because of how the bonds are formed. Now, while I did say always, the shape is not always visible to the human eye either because the crystal is too small to see or because other factors have disguised the shape. This happens often in nature as minerals all grow together, often into each other masking the specific crystalline shape of individual minerals. (If you’re in the lab course, you’ll see this when you complete the Mineral’s lab.)
Take a look at Figure 3.5 of your textbook (p 80). If you’re a decent geologist and happen to come across large distinct crystals, you can use the crystalline shape of a mineral to figure out which mineral it is! If you find a mineral that is shaped like an eight-sided diamond (Figure 3.5.1), then you could be pretty certain that you are holding either Fluorite or Kimberlite, the latter of which could make a nice engagement ring. Ever wondered why they call them diamonds? When geologists are in the lab, they can use advanced imaging methods like x-ray crystallography to look at how atoms are bonded together. (We have one of these instruments here at IUPUI and students use it to identify minerals in different rocks.)
So, here’s a question for you: Are crystals of sugar a mineral? (See the bottom of the next page for the answer.)