Geology Home Page
last edited: 10/15/15
Naturally formed crystals of halite (salt). The blue halite (sodium-rich)
crystals formed first and were later overgrown by clear salt crystals.
Growing nice crystals of common table salt is difficult for several reasons.
First of all, you cannot grow it by the supersaturated technique method because
the solubility curve is almost flat. In other words, by raising the temperature of
the water, you really cannot dissolve additional salt above the normal saturated
level. In the super saturation technique the excess chemical that was dissolved
at the higher temperature would come out of the solution as the temperature cools.
Alum works well with the supersaturated technique, table salt doesn't.
only way to grow salt crystals is by evaporation. Most commonly,
hundreds of tiny crystals form instead of just a few isolated crystals that become
seed crystals. It has been suggested that one should use pure salt, not iodized
salt because the iodine added to regular table salt favors the production of tiny
crystals. Sea salt or pickling salt should be used in trying to grow salt crystals.
is just pure salt.
It is also
important not to disturb the salt solution once it has been into a
growing container because the slightest ripple will cause small crystals to form.
Dust settling on the solution will also produce unwanted seed crystals.
The lighter cluster of salt crystals are floating at the surface of the evaporating
salt solution and tiny salt crystals have dropped to the bottom of the dark-colored
pan. The average size of these crystals is about 1 millimeter.
This is a closer view of the tiny cubic salt crystals that have settled to the
bottom of the pan.
If you allow allow all of the water in the pan of saltwater to evaporate,
this is what you get.
The salt crystals are all crowded
together, but you can still pick out reflections
off square crystal faces.
The last bit of salt water to evaporate produces a coating of even tinier salt
crystals on the earlier formed crystals.
Here is a closer view of the coatings.
The best salt crystals that I have seen grown were done entirely by accident.
For a science fair project a student put a tray of saltwater under a hot lamp to
demonstrate the evaporation process. He developed cubic crystals that were
larger than one quarter inch. Perhaps starting with a dilute salt solution with no
seeds in it, followed by rapid evaporation under a hot lamp might do the trick.
Another possibility for growing larger salt crystals might be to start with an
almost saturated solution of saltwater and then place a large cleavage fragment of
salt in the solution before small seed crystals start to form.
Here are some halite (salt) crystals that formed naturally by evaporation of
Searles Lake, San Bernardino County, California.
These salt crystals are actually pink in color.
experiment that you try with salt is to grow a "crystal garden".
Start with a saturated solution of salt. In other words dissolve as much salt as you
can in a half glass of water. Lightly stuff about 6 Kleenex tissues into the water until
the tissues reach the top of the glass. Put the glass away for two or three weeks
and forget about it. As the water slowly evaporates, crystal cluster will form above
the surface of the glass.
Looks almost like cauliflower.
The salt crystals were very tiny.