The Rock Cycle and Gemstones

It all starts with magma. The red hot liquid stuff inside the earth. Hotter and hotter as you go inside. Why, I wonder? As magma cools, rock is formed.

What’s a rock in the first place? Hard substance? Nope…

It’s a solid substance with certain molecular arrangements, keeping the particles bound together.

You’ve probably heard of this before! Igneous, Metamorphic & Sedimentary rocks.

But where do we begin? We can start from the weakest and follow its way to the strongest of the three. Sedimentary rock. Delicate. Used in construction. Sandstone. Wears down over time. Like the pyramids! 💀☠️

This sediment is washed down by water.

Water!

Another driver of this natural cycle. Sediment builds up in the rivers as they take them into the deep sea.

Sediment builds over time, then descends downwards.

Closer and closer to the magma. Increasing in temperatures & pressures to form metamorphic rocks.

Marbles is the word for metamorphic rock.

As one Raja said to the other:
Oi! Have you lost your marbles?
Spending all this on your Rani’s Tomb?

Some of this can descend to become magma again. All this descending stuff. [improve this transition] Did they find marbles in the deep sea? How are we mining it here on land? (intro music plays) bring in the tectonic plates…

Nature’s got it. [!] Nature’s trains. Powered by convection currents. Now keeping that in mind let’s get back to our magma.

Magma rising cools down to form igneous rock. Cooling magma causes crystallization of rock. The speed of crystallization determines the size of the crystals. Fast cooling makes smaller crystals, while slow cooling makes larger crystals!

Where exactly do gemstones fit into this picture? Igneous rock.

Pockets of magma, containing special compositions of ions cool down to form gemstones within the veins of the rock. Corundum, topaz, garnets, quartz. A slight change in composition, just a tiny bit. And it brings about all the change in its value.

These are some families of gemstones [move out to another article with link]

• Corundum (Al, O)
• Beryl (Be, Al, Si, O)
• Quartz (Si, O)
• Spinel (Al, Mg. O)
• Topaz (Al, Si, O, F)
• Garnet (Si,O)
• Tourmaline (Al, Si,O, Boron, other metal ions)

We’ve made a fun chart here trying to point out the elements responsible for forming some of those gemstones out there. Have fun figuring it out!

And here’s a picture from John Farndon’s book Rocks, minerals and gems.