| Chemical formula | Crystal type | ||
|---|---|---|---|
| Table salt - halite | NaCl | Face-centered cubic | |
| Salt substitute - Potassium chloride - sylvite | KCl | Face-centered cubic | |
| Regular Sugar - sucrose | C12H22O11 | ||
| Baking soda - Sodium bicarbonate | NaHCO3 | Monoclinic - Prismatic | Used to make bread rise instead of yeast |
| Alum | KAl(SO4)2·12H2O | Isometric - Diploidal | In the spice section, used in pickling recipes |
| Borax | Na2[B4O5(OH)4]·8H2O | Monoclinic - Prismatic | Used to wash clothes |
| Boric acid | H3BO3 | Trigonal planar | Eye wash - find on drug isle |
| Epsom Salts - Magnesium sulfate | MgSO4·7H2O | monoclinic | Foot baths, intended to soothe sore feet - find on drug isle |
| Sodium thiosulfate | Na2S2O3 | monoclinic | Hypo, used to develop photographs |
| Plaster of Paris - Calcium Sulfate | CaSO4·nH2O | orthorhombic | Your house is made of this |
Purity is not a requirement for growing crystals. One of the ways to purify a mixture of various substances is to grow crystals. The crystals are the pure substance, and the gunk (whatever else was present) gets left behind. However, this does not always work - sometimes you might get a combination of 2 types of crystals which are hard to separate mechanically (such as picking them out by hand). In other cases, crystals simply won't grow.
Studying crystals is an important part of physics, chemistry, and geology. Much of what we know (or at least, think we know) about the universe come from their study.
Coal Garden
In the past, homes used coal for heat - therefore, it was easy to obtain. However, any porous substrate will work - paper towels, sponge, whatever. The idea is to use something with good capillary action and lots of edges where water will evaporate - because that is where the crystals grow.
An old recipe is to start with a lump of coal. Add twigs (support) and Spanish moss (good evaporation). Add too much salt to some water, you want a super saturated solution. In theory, that is all you need. However, the traditional recipe also includes bluing and ammonia - like coal, both were common in the Depression.
Things with lots of pores will help the water evaporate faster. Some rocks have lots of pores - coal and limestone work. Paper towels are good, but need a support so they have an edge a bit above the solution..
A few drops of ammonia will reduce the surface tension so the water flows better and evaporates faster.
Mrs. Stewart’s Bluing is a colloidal suspension of extremely minute particles of blue powder (Ferric Hexacyanoferrate). When white clothes are washed a lot, they tend to turn yellow. In the past, adding an inert blue substance (bluing) to the wash made them look whiter simply because they reflected more blue light. In the store, I found some next to the bleaches. It even had a red and yellow sign on it
| Make a Salt Crystal Garden! |
False coloring is not a requirement, but many people like to add a few drops of food coloring. Don't put these in the bulk liquid - put them on a dry part of the garden.
Because they grow so fast, the crystals in a coal garden tend to be quite small. If you put a super saturated solution in a sealed jar, you will get larger crystals. It may take a month .. or two .. but the results can be impressive.
Some substances, like sugar, won't crystallize in a sealed jar. (Sugar plus water just becomes syrup.) In these cases, there needs to be something for the water to evaporate from. The common suggestion is a piece of string tied to a stick placed over the top of the jar. Do not seal the jar, just leave the top off. As long as the string is below the top, the rate of evaporation will be slower and larger crystals will form. Speed is the key.
When studying rocks, you will see lots of crystals. For igneous rocks, the longer it took for the original liquid to cool, the larger the crystals.