We use various types of crystalline rock salts to help prevent
water from freezing on roads and sidewalks in the winter. But
even more interesting, you can grow blue crystals from the salts
used as plant fertilizers; the bright blue color gives away the
presence of copper(II) ion in these products. Plant food containing copper sulfate is a mixture of compounds, including other
inorganic salts and organic chelating agents, such as ethylene-diaminetetraacetic acid (EDTA). Products in solid form that are
marketed to destroy roots near septic and sewer systems are
pure copper sulfate pentahydrate. Isn’t it interesting that the
plant food and the root killer are the same compound?
Crystals from kits
If you’d rather not raid your home for materials to use to grow
crystals, you also have the option of purchasing a crystal-growing kit. Inexpensive crystal kits are available for growing crystals
such as potassium phosphates. Some kits have dyes added to
the crystal-growing ingredients to make the crystal formations
more aesthetically appealing.
Growing crystals from an aqueous solution
Numerous recipes and demonstrations are available online to
help you get started. The key to growing crystals from an aqueous solution is to start with a supersaturated solution. You
may find that the degree of supersaturation has an impact on
whether you observe fast precipitation of microcrystalline powder or slow precipitation of large crystals. Temperature is also a
factor; the lower the temperature of the solution, the larger the
driving force for crystallization. Furthermore, dust or other solid
particles in the solution will initiate the growth of crystals.
From a thermodynamic standpoint, the larger the driving
force, the faster the crystals will nucleate and grow; this condition promotes the growth of many crystals simultaneously.
Thus, the growth of large crystals is a balancing act of achieving
growth — but not too vigorously. Also, many crystals growing at
the same time will exhaust the resources in solution, so it may
be beneficial to remove all crystals from the solution except the
desired ones. In the case of organic crystals such as sucrose, care
must be taken not to overheat the solution in order to avoid any
unwanted chemical reactions taking place. Moreover, because
of the high solubility of sucrose in water, supersaturated solutions are highly viscous, and thus slow cooling helps the sucrose
molecules to maintain sufficient mobility for crystal formation.
Once you’ve achieved success growing your crystals, you might
want to consider entering them in a crystal-growing contest, or
maybe your student chapter could host a contest. Take photos
at regular intervals, so that when you grow that one truly amaz-
ing crystal, you’ll be ready to share it with the world. You can
even film fast-growing crystals with your smartphone. Later,
you can share your photos and videos in a time-lapse presenta-
tion. Be sure to document the conditions used to grow your
crystals. Once you show your crystals to others, they may want
to grow similar crystals, and your documentation can be a help-
ful resource for them.
Studying and understanding the amazing crystalline state of
matter has resulted in many technological advances and Nobel
Prizes. It is no wonder that 2014 has been designated worldwide as the International Year of Crystallography. The science
and beauty of crystals is within everyone’s reach to explore and
enjoy. But the most wonderful thing about crystals is that there
are still many waiting to be discovered! For more information on
how to get started with your own crystal growth projects, go to
Camille Y. Jones is an experimental physical chemist
currently developing and teaching a new materials science
laboratory at the Columbia University School of Engineering
in the Applied Physics and Applied Mathematics
Department. For more details on her crystallography and
crystal growth projects, and additional resources on crystals
and crystal growth, visit www.crystallog.wordpress.com.
Understanding the art and
science of growing crystals
Good crystal growth depends on the control of many environmental variables. However, growing good crystals is also a bit of an art.
Be creative in your exploration of growth conditions, additives, and
crystallization sites such as pipe cleaners and wooden sticks.
THE SCIENCE BEHIND CRYSTAL GROWTH
In the aqueous solutions that are used to crystallize the common
compounds discussed in this article, it is the accumulation of
ions or molecules into the nuclei that eventually forms crystals.
This is an essential step in the crystallization process. The study
of nucleation and growth elaborates the thermodynamic driving
force and kinetics of the formation of crystals. In crystal growth,
Gibbs energy of surfaces opposes the process and Gibbs energy of
the volume of embryonic crystal advances growth. The balance of
these and other competing energies determines everything from
the rate of growth to the final shape of the crystal. Also, you can
vary the temperature or the composition of the growth solution to
enhance the growth of crystals or change their shapes.
Describing what your crystals look like is also part of the science.
Crystal morphology involves the systematic description of the
shape and size of a crystal and the relationship between these
qualities and the underlying structure and growth behavior at the
atomic level. For describing small crystals’ morphology, a magnifying glass, macro lens, or microscope is an essential tool. Be sure to
examine your crystals closely to describe their shape, size, color,
and transparency as accurately as possible.