Virtual Geology Museum
Hall of Minerals
Geology Home Page
geology instructor (email@example.com
last edited: 10/6/10 copyright 2010-R.Weller
mono ammonium phosphate crystals colored by yellow food dye
mono ammonium phosphate crystals colored blue by food dye
dihydrogen phosphate and potassium dihydrogen
phosphate (KDP) are also excellent chemicals for growing crystals. These
chemicals are not available in drug stores or hardware stores and therefore must
be ordered from chemical supply companies. These chemicals work well by either
supersaturation or saturation techniques.
One of the commercial growing kits, The Smithsonian, uses mono ammonium
phosphate in half of the experiments and potassium alum in the
Mono ammonium phosphate produces crystals in the Tetragonal system of
crystal symmetry. The most common crystal form is a four-sided, long column
capped at each end by four-sided pyramids.
Because this crystal of mono ammonium phosphate grew in a cluster,
the 4-sided pyramid did not form at the other end of the crystal.
At different stages in its growth, this crystal of mono ammonium
phosphate developed imperfections. Consequently the different stages
in its growth can be observed. This type of crystal in which stages can
be observed is referred to as a "phantom crystal".
In its pure form, mono ammonium phosphate is colorless and
A crowded cluster of mono ammonium phosphate crystals
A closer view of the cluster of mono ammonium phosphate crystals
These colorless crystals are quite beautiful, but if you want to jazz up your
specimen, you can put a large quantity of food coloring in your growing
following photos are of mono ammonium phosphate crystals that were
grown by the evaporation method in an almost opaque solution containing
a dark blue food coloring.
color almost makes these crystals look like copper sulfate,
but the crystal shape identifies the material as mono ammonium phosphate.
Crystallization is a purification process. Notice that the tips of the crystal are clear
and colorless and have been able to exclude the blue food coloring even though
the growing solution was an extremely dark blue color.
photomicrograph of trapped dye solution in mono ammonium phosphate crystal
closer view of the above specimen
The crystal is clear, color comes from pockets of dye in solution.
mono ammonium phosphate colored yellow by food dye
closer view of the previous specimen
web link for potassium dihydrogen phosphate (KDP)
VIDEO: Growing KDP Crystals