By Nick

The Green Machine

Deep in the basement of the department lies the Green Machine. No, we’re not keeping two of Canberra’s finest rugby league players, Terry Campese and Josh Dugan, captive. But the similarities are striking. Our Green Machine is also designed to withstand high-pressures, stands a couple of metres tall, is built pretty solidly and is decked out in garishly 80s colours.

This is a high-pressure, high temperature rig. A machine designed to exert huge pressures and temperatures on small pieces of rock, in an effort to recreate conditions deep inside the earth. Its often used in the department to understand how rocks react to stresses, to see how they break, to see how minerals, fluids and elements migrate and react at higher temperatures. I, however, use it for making my very own rocks.

You see, I ran into a problem. I needed a rock or mineral, made mainly of calcium carbonate (limestone), with a known amount of sulphur in it and with this sulphur distributed evenly throughout. Apparently these things just don’t exist. So I decided to make it myself.

I ground up some spare flowstone offcuts (kind of a sideways growing stalagmite) that no-one seemed to be using in a pretty cool automatic pestle and mortar. I added some calcium sulphate, and ground it up some more. And then did some more grinding by hand. The powder has to be extremely fine in order for the sulphur to migrate through the rock under high temperatures and homogenise.

The inner workings of the high-pressure rig. The hole in the middle is where the sample is slid into the machine.

I then pressed the powder into two small pellets using a mere 200 megaPascals of pressure (that’s barely 2000 atmosphere’s worth!). These two pellets were then loaded into a metal jacket and into the high-pressure rig, which has lots of cool old-fashioned dials, and twisty handles, and printouts and such that make you feel like you work in a real laboratory.

The kind of machine set-up that makes you want to cackle and take over the world like some kind of evil super-villain.

We then took the pressure up to a whopping 600 MegaPascals, that’s 5921 times air pressure and equivalent to being buried under 22km of rock. The temperature was increased to a relatively modest 600 degrees C. We then left the set-up for 24 hours. This gives time for all of the crystals to fuse together, to grow into each other and for the sulphur to migrate (hopefully) through the system.

A sliced open pellet of synthetic marble

The result: I have created my very own rock, a synthetic marble. Very cool eh!