By Ella Murphy
All about Crystals!
1. What is a crystal?
A piece of a homogeneous solid substance having a naturally geometrically regular form with symmetrically arranged plane faces.
2. What substances can be used to make crystals?
There are many many substances that can be used to make crystals such as;
aluminum potassium sulfate, ammonium chlorid, sodium borate, calcium chloride, sodium nitrate, copper acetate (cupric acetate), copper sulfate (cupric sulfate), iron sulfate (ferrous sulfate), potassium ferricyanide, potassium iodide, potassium dichromate, potassium chromium sulfate (chrome alum), potassium permanganate, sodium carbonate (washing soda), sodium sulfate, sodium thiosulfate, cobalt chloride, ferric ammonium sulfate (iron alum), magnesium sulfate, nickel sulfate, potassium chromate, potassium sodium tartrate, sodium ferrocyanide, sodium chloride, sodium bicarbonate, silver, bismuth, tin, monoammonium phosphate, sodium acetate, calcium copper acetate
3.What are some examples of crystals in nature? What household items can you also grow crystals from?
Crystals in nature include rocks, ice and salt crystals when the sea dries out. Items such as salt, sugar, vinegar and washing products can be used to make crystals.
4. Explain how crystals can grow in different shapes and sizes.
Crystals grow in a distinctshape that differ according to each crystal because of the chemical structure and properties atoms and molecules.
5. Outline a few different types of crystals.
There are many types of crystals, which are categorized into mainly two groups; the group that is recognized by lattices (shape)and the other is grouped by its properties.
Grouped by Lattices (shapes)
Cubic or Isometric, Orthorhombic, Hexagonal, Trigonal, Triclinic, Monoclinic.
Grouped by its properties
Covalent Crystals, Metallic Crystals, Ionic Crystals, Molecular Crystals
6. What are the optimum conditions for crystal growth?
For your crystals growth you should consider that the substance that your crystals are growing in it must be supersaturated with it for crystals to grow. The temperature for the crystals is also very important because warmth is key to forming crystals. The jar's surroundings should be warm for optimum crystal growth. Warm air temperature aids water evaporation, causing the crystals to grow more quickly. Crystals will still grow in cooler temperatures, but it will take much longer for the water to evaporate.
Crystal growth also requires light. The crystals will eventually grow in the dark, but it will take a very long time. Light evaporates water as heat does; combine them by placing your jar on a warm, sunny windowsill and you should have crystals in a few days.
Method and Materials
- 250ml beaker
- -a filter funnel
- -filter paper
- a source of hot water
- -a stirring rod
1. Make sure all apparatus is clean and dry.
2. Place approximately 25 g of potash alum in a beaker (250 ml or bigger) and add approximately 170 ml of hot water.
3. Stir the mixture until all the crystals have dissolved. The solution may have a slightly cloudy or milky appearance due to impurities in the technical grade of alum used.
4. Filter the warm solution through a filter funnel (in which filter paper has been inserted) into another clean beaker.
5. Cover the beaker of solution with fresh filter paper and set aside in a cool sheltered place and allow it to stand undisturbed overnight.
6. The first beaker and funnel can be washed and dried and the residue and filter paper used for filtration discarded.
- 250ml beaker
- plastic spoon, spatula, tongs or tweezers
- a smart phone or digital camera
1. The next day, observe the beaker of solution. The bottom should have become covered with a layer of smallish crystals which formed spontaneously as the solution cooled.
2. Carefully pour off the clear solution above the crystals into a clean beaker and set it aside for later, leaving the crystals behind in the other beaker.
3. From the bed of crystals, one good symmetrical crystal or group of crystals needs to be selected to act as “seed” for your big crystal.
4. Using a plastic spoon, spatula, tongs or tweezers, transfer the selected crystal to the beaker containing the decanted solution, trying to place it centrally in the beaker.
5. Take a picture of the crystal, preferably close to a ruler so that you can measure its size, and mark the level of the liquid in the beaker. Record the date in your diary.
6. Cover the solution with a loose-fitting paper hat that permits water to evaporate slowly whilst keeping out dust.
- a smart phone or digital camera
Allow the solution to stand and weekly record in your diary the level of the solution in the beaker and if possible, without disturbing your crystal, take a picture of it close to a ruler so that you can estimate how much it has grown.
Try and avoid disturbing crystals during the growth phase as this may induce additional crystals to grow.
Continue to monitor progress by reporting on the drop in water level, and estimate the size of the crystal.
Refer to photos below of crystals made in class
Holiday Crystal log
In this week both the two crystals growth rates have been quite low. They have been sitting on a bench inside, not exposed to sun light or much warmth. It appears that the two major crystals have barely visually grown, however the various other small crystals **have grown more and their growth rate in higher. In the second week I am experimenting with the change in conditions, moving the jar to a sunnier, warmer area to determine if that will effect the growth rate of the crystals. The shape of the crystals has seemed to have become a lot more sharper and more facets have seemed to have shaped. Both the crystals have seemed to become more flat and less pyramid like. Perhaps their growth has mainly been on the sides of the crystals which has flattened the top of the crystals. One crystal has shaped to a hexagonal shape, where as the other crystal has shaped to be more triangular, however strangely it . The two crystals were originally different heights but it appears that they are both now very similar in height.
The level of solution in the jar has slightly decreased, but because the jar has not been exposed to sunlight and warmth it's evaporation rate is reduced. It's original level at the beginning of week one was 18.5 mm, but at the end of the week it sat at 17 mm. Hopefully with the crystals conditions changing in week 2, the evaporation rate and there for the growth rate will increase.
**Note that these crystals were formed due to vibration of the jar and are very small
Refer to photos below of the crystals during the beginning of the first week.
Refer to photos below of the crystals during the end of the first week.
This week I have had the crystals exposed to natural sunlight and warmth (although it hasn't been very warm at times throughout the week). The crystals growth has increased, quite evenly . The crystals are now a lot less flat and this week they have grown a lot. If we compare the photos of mid week 2 to the end of week 2, we can see that the height of the crystals is significantly different. The smaller crystals that were formed due to vibration have also increased in size and they have now formed a clump of small crystals. This week the growth rate has impressively increased.
It appears that most of the growth this week has been between the end of the first weeks and mid week in the second week. In those times I saw a dramatic change in size and 2 mm of solution evaporated. The solution went from 17 mm to 15 mm in a matter of 3 days. This over powers week one which lost 1.5 mm in 5 days. However I believe that the evaporation rate would have increased if the weather had of been warmer. In the second half of the second week only 1 mm of solution was evaporated in 3 days (the solution dropped from 15 mm to 14 mm) and I believe that this was partially due to the lack of warmth.
What is most interesting is that during the first half of the week the evaporation rate increased and during the second half of the week the growth rate increased. Perhaps the absorption of sunlight and warmth in the first half of the week encouraged growth rate in the second half.
Refer to photos below of the crystals during midweek of the second week.
Refer to photos below of the crystals during the end of the second week.
The final Conclusion
Refer to photos of the final crystal artworks.
These crystal artworks demonstrate the properties of the crystal, by the refraction of the light that passes through them. This is what makes the crystal shine and because of this I believe they appear attractive.
Crystal 1 and 2
Crystal 1 is the biggest crystal out of the 2. They both have hexagonal shapes on one side, however on the other it represents more of a triangle, especially in crystal 2. Crystal 1 has small vibration crystals growing off of it and both have scratches and marks due to vibration during their growth. Through out the 2 weeks they have grown in height, width and length. From the beginning of the experiment the crystals have changed from a square shape to a hexagonal shape and a triangular shape. The edges and facets of the crystals have become more sharper and distinct as well.
The vibration crystals may have been the reason that the crystals growth was stunted. The day that I took the crystals home I had to take them to the park with my exchange student. We had to walk to the park and I believe that is when the vibration crystals were formed. They grew over the 2 weeks perhaps more then the major 2 crystals and formed a large clump in a semi circular shape (due to the edge of the jar).
Refer evaporation rate table above
Activity sheet below