If they have changed color or formed crystals, throw them away and get new ones.
For one thing, many proteins do not readily form crystals.
If you go too slowly, it will form crystals.
Under certain conditions they form crystals which retain their structure indefinitely.
When sugar or salt falls out of solution, it forms crystals you can see.
In this process, some minerals form crystals, then settle to the bottom of the chamber.
Granite has a slow cooling process which forms larger crystals.
The I2 will tend to sublime and form new crystals on the walls of the container.
These compounds can be melted together and form mixed crystals of one dissolved in the other.
It also combines with other elements to form powders or crystals.
