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Gemstones are rare crystals which have valued for their appearance. They form under specific conditions within the earth’s crust as magma moves around and cools. Each type of gem is unique, with a distinct appearance and properties.An image showing many types of gemstones.

What is a Gemstone?

You’ve probably seen a gem before. But, it’s quite difficult to tell them apart from non-gems. Let’s test your knowledge. Is this a gemstone?

An image of rose quartz crystals.

Rose quartz.

While it’s pretty, the answer is no. This is rose quartz, a common mineral. And if you couldn’t tell it apart from a gem, that’s alright. It’s not always clear what is a gem and what’s not. But, to help us better understand, we can examine their structure.

Crystal Structure

Gemstones are crystals. This means that they’re made up of atoms which arrange themselves in a repeating pattern. For example, the crystal which makes up salt is just alternating sodium and chlorine atoms. They’re organized almost like the spots on a checkerboard.

An image showing how atoms are structured in salt.

The structure of a salt crystal. This simple pattern of alternating sodium and chloride atoms makes up salt.

Salt isn’t a gemstone, of course. Otherwise, it would be very expensive to make most foods! But, the crystals which make up gems aren’t so different from the ones that make up salt. So, why is it that gemstones are so valuable?
For one, they have a special appearance. People like to put gemstones in jewelry. But, there are also plenty of things that look nice that aren’t so valuable. For example, pyrite is a very shiny mineral which is worth almost nothing.

An image of pyrite, a worthless mineral.

Pyrite, a worthless mineral.

So, we have to ask a different kind of question to understand why gemstones are valuable.

What are Gemstones Made of?

As we’ve discussed, gems are crystals. But which elements, or kinds of atoms, are in them? The answer depends on which gemstone we’re talking about. In fact, the composition of a gemstone is part of what makes it unique.
But, the crystal pattern of these elements matters a lot, too. Even if they’re made up of the same element, crystals can be totally different. One of the most famous gemstones is diamond. It’s made up of only carbon. And you know what else is? Pencil lead.

An image of a pencil writing on a piece of paper.

The stuff in diamonds.

That’s right. The only difference between pencil lead and diamond is how their crystals arrange themselves! Clearly, the difference matters a lot. Let’s learn a little more about how these crystals form.

How are Gemstones Created?

The process of gem formation is, simply, crystallization. It’s what happens when hot magma starts to cool off. Magma is actually made of a lot of different things. It collects all sorts of minerals as it melts its way through the mantle and crust.
Yet when it starts to get colder, it can’t hold as much stuff. Certain elements begin to leave the magma in the form of minerals. Minerals are basically solid groups of atoms (like sodium and chloride). Most minerals aren’t too valuable. These makeup igneous rock. But, some minerals can be converted into gemstones.
Beneath earth’s layers, there’s a lot of heat and pressure. This can force rocks and minerals into certain crystal patterns. Different combinations of heat and pressure create different crystals. It’s like there’s recipe for each. A very small amount of these ‘recipes’ can create gemstones.
As you can see, it takes a whole lot to make a gem. So, we’d better know when we find one! We’ll talk about how we identify gemstones next.

How to Identify a Gemstone

Types of Gemstones

Gemstones are usually classified first by their color. That’s how they’re sorted here. Although, sometimes gems look pretty similar. The same gem can even come in different colors! If you’re interested in how to identify them beyond color, check it out this great video.
For right now, we’ll stick with color. There’s a list with a few gems of each color below. You can click on their names to see pictures of them.

Blue Gemstones

Two blue gemstones are aquamarine and lapis lazuli. 

Green Gemstones

A famous green gemstone is emerald. Another one is jade.

Purple Gemstones

One common purple gem is amethyst. Less common is ametrine.

Red Gemstones

Ruby is the most well-known red gemstone. Garnet can also be red.

Other Great Resources:

Awesome Gem Encyclopedia for Kids: http://gemkids.gia.edu/

Broader Gemstone Wiki: http://www.minerals.net/GemStoneMain.aspx

Video on Minerals: https://www.youtube.com/watch?v=8a7p1NFn64s

Video on Crystal Formation: https://www.youtube.com/watch?v=rQB4Hwi4O-M

Make Crystal Candy!: https://www.gemsociety.org/article/gem-formation/

Written by: Noah Louis-Ferdinand