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Experiment 5: Microcrystals Under the Microscope

From JoAnne Nelson (British Columbia Geological Survey)

Discussion.

In this experiment crystals of colored metal compounds are grown in drops of water on glass slides and observed with a microscope. It only takes about 30 minutes for a drop of water with chemicals dissolved in it to completely dry up and crystallize.

What you need.

  • Biological (transmitting) microscope. This is the type of microscope designed to view slides with illumination from below the stage.
  • Glass slides.
  • Dropper bottles containing a saturated solution of any water-soluble transition metal compound such as Copper Sulfate, Ferrous Sulfate, Calcium Chloride.

What to do.

Place a clean, blank slide on the microscope stage. Put a drop of solution on the slide (do not cover) and turn the microscope light on. Heat from the bulb will speed evaporation and hasten crystal growth. Check the slide every two minutes or so and watch what happens!

What can be learned.

This experiment models the growth of natural crystals like quartz, only on a very compressed time scale. Quartz crystals in nature probably grow over thousands of years.

The round water droplet is like a cross-section of a natural geode, especially with the crystals that grow in from the sides. Geodes in nature form in holes in the rock.

Each compound or mineral has its own characteristic crystal form. Size doesn't matter: form does. Try sketching the various crystals that grow from different solutions. Other solutions to try are salt and sugar. Salt forms little cubes, while sugar crystals are less symmetrical, with less right angles between faces.