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An ore is a chunk of mineral. They are often mined for a profit. It is a totally man-made concept. We only call a rock an ‘ore’ if it’s valuable to us. That said, valuable materials group up in rocks through several processes. The main one is the cooling of rising magma from Earth’s mantle.

An image of a miner holding a piece of ore.

A miner holding a piece of ore.

What is Ore?

There are so many different types of rocks and minerals found underground. So, it can be hard to tell which is which. Lucky for us, it’s a very simple and broad category. It can include anything from common metals to gemstones.
To give a clear definition, ore means rock which contains a cluster of valuable materials. This generally implies that there has to be a lot of minerals in a pretty small area. Otherwise, they wouldn’t be worth that much.

What Does Ore Mean?

The word has a long history, but it just means unprocessed metal. When we talk about it, we’re usually referring to types like iron and aluminum. Both of these can be processed into useful metal. For example, hundreds of millions of tons of raw iron make their way around the world each year. Most of it’s converted into steel, a very durable metal.

An image of stacked steel tubes.

Stacks of steel rods. Steel is the processed form of iron ore.

Metal Ores

And while we’re talking about processing, we should make another distinction. There are actually many different types, each with a different rarity. The most common types are those which give us metals used for building, like iron. Other kinds are harder to find.
To give an example, diamond ore is extremely rare. Also, when we find it, it’s only in small amounts. The same thing is true of rare gems and ‘precious metals’, like gold.
Of course, in order to find any of these, we need to know how and where they’re made. We’ll review what we know about ore formation next.

How is Ore Formed?

While the creation of every type is different, each follows the same basic process. This process includes three steps: sourcing, transport, trapping.

Sourcing is really a very simple step. It just means that the minerals have to come from somewhere. Ideally, this place will have a lot of minerals. But, they’ll be too spread out to be useful. Such mineral-rich places form and open up because of plate tectonics. This happens very slowly. So, most ‘sources’ on earth have already been created.

An image of rocks which contain minerals but aren't ores.

These rocks probably contain minerals. But, they are so spread out that we can’t see them.

Next, minerals in a source need to move to a new place. This happens in a few ways, though most often by the action of magma or water. These fluids move through rocks and dissolve (or melt) the minerals in them. Then, somewhere else, the minerals will leave the fluid. We call this recrystallization. If enough of the mineral recrystallizes in one area, an ore forms.
Yet, this can only happen in certain places. We call the spots where recrystallization happens ‘traps.’ After traps fill with minerals, we call them ‘ore veins’.

Ore Veins

The last part of ore formation, trapping, requires a special environment. There, a large number of minerals will recrystallize all at once. If they did so slowly, we wouldn’t have the cluster we call an ore.
But where is best? That question matters a lot because it tells us where to find valuable resources.

The answer is that it actually depends upon the ore we’re looking at. To give an example, diamond ore only forms veins in a limited number of places within the crust. It’s transported from the mantle to these specific spots over millions of years. Oppositely, gold ore gets trapped by tectonic events up in the lithosphere. As a result, we find gold veins in a much wider range of places.

An image of unprocessed, green malachite ore.

The mineral trapped in this vein is malachite.

So, sadly, there isn’t one kind of place where ore becomes trapped. Although, wherever they are, you can be sure to find a mine!

Ore Mines

The fact that ore forms close veins makes it ideal for mining. Ore mining is a huge field, so we can’t say too much about it here. But, if you’re interested in learning more, check out this video as well as the resources below:

Other Great Resources:

Ore Facts by Kiddle: https://kids.kiddle.co/Ore

More about Iron Ore: http://www.ironorefacts.com/the-facts/basic-iron-ore-facts/

History Channel Documentary on Diamond Mining: https://www.youtube.com/watch?v=f48PopFqzNk

Why do Minerals Crystallize/Recrystallize?: https://www.basd.net/cms/lib2/PA01001269/Centricity/Domain/353/Ch_4_Sec_2_How_minerals_form.pdf

Written by: Noah Louis-Ferdinand