February 2013

Crystal Conundrum

Is this a Kryptonite crystal?

Answer

Copper Sulphate crystal formed around a copper wire, on display in the Discovery Centre (Level 3). copper sulphate Close up view of copper sulphate crystal

Although this specimen is reminiscent of the fictitious radioactive Kryptonite, it is actually an impressive example of the Copper Sulphate crystal.

Crystals form when dissolved molecules of a salt or mineral are present in such high quantities that the solution becomes saturated (i.e. no more of the salt or mineral can be dissolved into the surrounding liquid). 

The temperature of the liquid determines how much salt or mineral can dissolved into solution. At higher temperatures more of the salt or mineral can dissolve; so as the liquid (or solution) cools it becomes supersaturated, beyond the carrying capacity of the liquid. In this environment crystals are most likely to form.

Crystals need a tiny nucleus to start the formation process. This nucleus can be as small as a speck of dust. Once that first tiny crystal has formed, more molecules of salt or mineral will continue to come out of the liquid and form layers on that first tiny nucleus. Crystals grow a little bit like the layers on an onion and eventually can become very large under the right conditions.     

The copper sulphate crystal that we have on display in the Discovery Centre was found in a disused copper mine in North West Queensland. Over time, large quantities of the ore had dissolved into the standing water to form a copper rich solution. The copper wire, being submerged in the undisturbed water, provided a good surface for the crystal to form on.

While this copper sulphate crystal might not have any impact on the man of steel, this trace element can be mildly toxic or irritating to humans if ingested or absorbed in large amounts through the skin and eyes. It is commonly used in agriculture to inhibit fungus growths on crops. It can be used as a herbicide to control aquatic plant pests, and to inhibit root growth of terrestrial plants in pipe work. Copper sulphate is also used to create blue colour effects in fireworks.

You can make your own crystal at home with some simple equipment.

You will need:

  • Table salt (you can also use suger or epsom salt)
  • Clean glass jar
  • Thread
  • Icy pole stick
  • Saucepan
  • Water
  • Different coloured food colouring

Instructions (get an adult to help you with the boiling water)

  1. Tie your piece of string to the centre of the Icy pole stick
  2. Ask an adult to help boil some water in a saucepan. Stir salt into the water until no more can be dissolved. This is usually indicated by salt collecting at the bottom of the pan.
  3. Try adding different food colours to your boiling water to make different coloured crystals.
  4. Carefully pour the salt solution into the jar
  5. Place the Icy pole stick across the mouth of your jar, making sure that the string does not touch the sides or bottom of the jar.
  6. Place the jar in a stable place where it can be easily viewed, and remain undisturbed. Don’t put the jar in direct sunlight, this will warm the water and your crystal will dissolve back into the water.
  7. You should be able to see the crystals beginning to form after a day or two.

Queensland Museum's Find out about... is proudly supported by the Thyne Reid Foundation and the Tim Fairfax Family Foundation.