Ammonium dihydrogenphosphate for which the shortcut "ADP" is used, was and also is grown in large single
crystals on a commercial scale. They are used in piezoelectric devices, as frequency doublers in laser optics and
for there ferroelectric and optoelectric properties.
Since this material is cheap and not toxic its also widely used for hobby crystal growth. Its not as easy to grow
as alum but the results are worth some efforts.
Very strange is the capability of ADP to include large amounts of chromium(III) into its crystals lattice, which results in
a green coloring (in spite the fact that chromium(III)salts in aquous solution are red to purple !).
The chromium content of the solution is also helpfull to grow better developed crystal tips.
This specimen is currently exhibited at the mineral museum in Pforzheim
