Crystal Formation Task
What is a Crystal?
A crystal is a solid material that is formed by a consistent frequent pattern of molecules connecting together to make a solid object. The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation is called crystallization or solidification.
What substances can be used to make crystals?
Substances that can be used are:
- aluminium potassium sulfate
- ammonium chloride
- sodium borate (borax)
- calcium chloride
- sodium nitrate
- copper sulfate
- iron sulfate (ferrous sulfate)
- potassium iodide
- sodium carbonate (washing soda)
- sodium sulfate, anhydrous
- potassium chromate
- potassium sodium tartrate
- sodium ferrocyanide
- sodium chloride (table salt)
- table sugar
- sodium bicarbonate (baking soda)
- sodium acetate (hot ice)
What are some examples of crystals in nature? What household items can you also grow crystals from?
Snowflakes, mineral crystals (gemstones), stalactites and stalagmites are a well-known example of crystals in nature. Household items you can used to grow crystals are:
- Sodium Carbonate
- Table Salt
- Sodium Chloride
- Sodium Bicarbonate
- Table sugar
Explain the process of crystal growth.
The formation of solid crystals is called nucleation. In the
nucleation stage, the molecules detached and gather to create clusters. If the
clusters are stable, they become the centers where crystals will grow. If the
clusters are not stable, they redissolve. Therefore, the clusters need to reach
a critical size to become stable nuclei. The critical size is dictated by the
operating conditions, such as temperature and super saturation (Super
saturation is the driving force of the crystallization process, controlling the
rate of nucleation and crystal growth). It is at the stage of nucleation that
the atoms become arranged into the crystal structure.
Explain how crystals can grow in different shapes and sizes.
More complicated cases (and shapes) happen when the crystal doesn't have equally perpendicular axes, and when the fastest directions of growth correspond to face or body diagonals (or even other directions) in the crystal.
Crystals grow at different rates in different directions is because if there is a highly attractive interaction along a certain direction of a crystal, then that direction will probably grow faster than another. However, it could also grow slowly.
Outline a few different types of crystals
There are 7 main types of crystals:
Triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes
Monoclinic - like tilted tetragonal crystals, often forming prisms and double pyramids
Orthorhombic - like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms or dipyramids (two pyramids stuck together)
Tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms
Trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division
Hexagonal - six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon
not always cube shaped. You'll also find that they have octahedrons (eight
faces) and dodecahedrons (10 faces).
What effect do crystals have on light travelling through them?
When a light trazels through a crystal the light disperses revealing the colours of the spectrum. The light also bends over the critical angle inside of the crystal and causes total internal reflection and the makes the light refect off the inside face of the crystal and making many reflections of the light shine out of the crystal.
What are the optimum conditions for crystal growth?
Supersaturated Solution (Saturated Water):
- Dissolve as much of your material into your water as possible
- Materials dissolve faster in warm water, so it works better than cold, since the molecules move more in warm water.
- Pour one spoonful of your material at a time into the warm water and stir vigorously until it disappears.
- When your materials no longer disappear and settle on the bottom of your jar, the water is supersaturated.
- Absorbent materials work best as foundations for your crystals to grow easily.
- The air spaces allow the dissolved material to gain plenty of surface on the foundation material and attract more dissolved material as the water evaporates and leaves the solid crystals behind.
- Rough bamboo skewers, yarn, thread, ice cream sticks, pipe cleaners and even fabrics work very well as crystal foundations. Pencils, paper clips and other very smooth, dense materials will not work because there is nothing for the crystals to grab onto.
- Nylon thread and fishing line only work if you tie a seed crystal to the end; even then, the crystal will grow in one place instead of climbing the material.
Light and Temperature:
- Warmth is the key to forming crystals; the jar's surroundings should be warm also for best possible 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 like heat does
- Place your jar on a windowsill and you should have crystals in a few days.