How Gemstones Form Inside The Earth

by Vidya Lakshmi January 24, 2021 4 min read

How Gemstones Form Inside The Earth

Hello again, fellow gemstone enthusiasts! Navinee is back again with yet another super interesting post. We’ve seen and talked about all sorts of gemstones on here. We’ve talked about gemstones for each month of the year, we’ve seen myths that surround certain gemstones, and we’ve also talked about how some of them were discovered. Haven’t you wondered how these gems were actually formed inside the earth? That’s exactly what we’re gonna talk about today. 

So today’s post is gonna be a little scientific, the actual processes and some reactions that take place inside the earth, which cause these beautiful gemstones to form. Trust us! This is not gonna be boring!

Let’s start with a little experiment, shall we?

What happens if you mix some sugar with water? It dissolves right? But if you keep adding in more sugar, the water reaches a point where it cannot dissolve any more sugar. What if we start boiling that water at this point? It’s gonna be able to dissolve more sugar now. Now we keep adding more sugar to this boiling water. It will again get to a point where it doesn’t dissolve any more sugar. Now we take the water off the heat and let it cool. If we insert a piece of string into the water as it cools down, all the extra sugar that it couldn’t dissolve at room temperature will form crystals around the string. This is pretty much how some gemstones are formed.

Alright, now that we’ve got that covered, let’s just refresh our memories and have a look at the different layers of the earth. We'll need this if we want to understand what happens inside of it.

The Crust

This is the outermost layer of the earth and is made of solid rock.

The Mantle

The mantle is 2900 kilomtres thick and lies right below the crust. 

The Core

The core is the centre of the earth. It has two parts, a liquid outer core which is about 2200 kilometres thick and a solid inner core which is around 1270 kilometres thick

And by the way, theres also tectonic plates - They are like pieces of a puzzle and constitute the upper mantle and the crust of the earth. There are a total of 7 major tectonic plates that make up close to 95% of the earth’s surface and several smaller ones that make up the rest. These are said to be in motion all the time and they have been so for quite a long time, very early in earth’s history. 

crust, mantle, core

Image Source : Thparkth at English Wikipedia, Public domain, via Wikimedia Commons

Remember everything now?

Okay, so there are four kinds of gemstones that can form inside the earth:

Igneous

These gems are said to be created deep inside the mantle of the earth and they require extremely high temperatures to be formed. The most prominent examples of these kind of gems are diamonds and peridot. Geologists say that diamonds are crystallised right below the earth’s crust as magma pushes up to the surface at an extremely high speed. 

diamonds

Image Source: Swamibu, CC BY 2.0

The gems are brought further up during volcanic eruptions and erosions. That’s how they can be mined.

Hydrothermal

These gems are formed in a very similar manner to the experiment we did earlier; by the cooling down of water. As water that is super saturated with minerals, is pushed up into the cracks in the earth, it cools down a bit more and the minerals present in it, crystallise. The beautiful emeralds mined in Columbia are formed in this manner.

emerald

Image Source : Ryan Salsbury, CC BY-SA 3.0 

Metamorphic

A majority of gemstones we know are formed in this manner. You probably already guessed from the name that the formation includes some sort of metamorphosis or change. Some minerals may be forced to join togther by the extreme heat and pressure caused bu tectonic plates  moving under each other. When two different minerals join together, they form an entirely different mineral or gemstone. Sometimes, these minerals fuse even without melting, because of the extreme pressure. Sapphires, rubies and garnets are formed in this manner.

sapphire

Image Source : Sapphiredge, CC BY-SA 3.0

Sedimentary 

These kinds of gems are formed when water collects minerals from the surface of the earth and seeps down through its cracks. As the water travels down, it deposits these minerals which form layers on top of each other and create gemstones.

Opal gemstone

Image Source: YippeeD, CC BY-SA 4.0

Opal is one gem that is formed this way. It's formed when layers of silica deposit on top of each other.

So that’s everything we have for you today. Hope you enjoyed reading this post as much as we did, creating it. See you soon with another interesting read. Until then, Bye!

Have a look at some of our popular jewelry too, before you go. Thanks again, guys!

Beatrice Butterfly Necklace

 

Morpho Cuban Choker

Morpho Cuban Bracelet


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