By Saffia Phipps Booth
What is a crystal?
Crystals are a special kind of solid material where the molecules fit together in a repeating pattern. This pattern causes the material to form all sorts of unique shapes.
What substances can be used to make crystals?
In nature, crystals can form when liquid rock, called magma, cools. If it cools slowly, then crystals may form. Many valuable crystals such as diamonds, rubies, and emeralds form this way. Another way crystals form is when water evaporates from a mixture. Salt crystals often form as salt water evaporates.
What are some examples of crystals in nature? What household items can you also grow crystals from?
Crystals in nature can be found in rocks such as granite, marble, quartzite, limestone, sandstone and shale. Not only rock but also ice. Snowflakes are considered a single crystal. Glaciers and icicles are also types of crystals. Household products are a pickling spice called alum, salt and sugar.
Explain the process of crystal growth?
The process of crystal forming is called crystallization. Crystals often form in nature when liquids cool and start to harden. Certain molecules in the liquid gather together as they attempt to become stable. They do this in a uniform and repeating pattern that forms the crystal.
Explain how crystals can grow in different shapes, sizes and colours?
Crystals grow in different sizes and shapes mostly depending on the rate of growth. Different crystals grow at different rates and in different patterns. The colour can depend on the temperature of the climate the crystal is growing in.
Outline a few different types of crystals?
Covalent Crystals: This is a crystal which has real chemical covalent between all of the atoms in the crystal. So really a single crystal of a covalent crystals is really just one big molecule. An example of this is a crystal like diamond or zinc sulfide. Covalent crystals can have extremely high melting points.
Metallic Crystals: Individual metal atoms sit on lattice sites while the outer electrons from these atoms are able to flow freely around the lattice. Metallic crystals normally have high melting points and densities.
Ionic Crystals: This is a crystal where the individual atoms don't have covalent bonds between them, but are held together by electrostatic forces. An example of this type of crystal is sodium chloride (NaCl). Ionic crystals are hard and have relatively high melting points.
What effect do crystals have on light travelling through them? (relate to reflection, refraction, dispersion and diffraction)
When light travels through a crystal, it is refracted. When travelling from a less dense medium into a crystal, the light bends towards the normal. When the light exits the crystal, because of the many faces, the light disperses in different directions.
What are the optimum conditions for crystal growth?
The optimum growing conditions are warm surroundings, including warm solution and warm air temperature. Crystals will still grow in cooler temperatures, but it will take longer for the water to evaporate. Crystal growth also requires light but the crystals will eventually grow in the dark, but it will take a very long time.
-2 x 250 mL beakers
- Filter Funnel and Filter Paper
- Stirring Rod
1. Put 25g of potash alum and 170mL of hot water into beaker
2. Stir until particles dissolve
3. Filter solution with funnel and filter paper into clean beaker
4. Cover solution with filter paper and allow to stand overnight
Only continue with this method if there are no crytals in the bottom of your beaker
- Potash alum
1. Carefully pour extra mixute off the crytals and put into beaker
2. Cover and allow to stand over night.
- Nylon Thread
- Stirring rod or pencil
1. Choose one small crystal as ‘seed’ for main crystal
2. Place selected crystal into jar
3. If you want, tie nylon thread around crystal and then suspend over jar using pencil or ord.
4. Take picture with ruler next to it.