Hi Karen. Green “amethyst” is gemologically known as prasiolite. It
is a variety of quartz, actually amethyst that has been heated to
change its’ color, just as it is heated to yield citrine. Strictly
speaking, only quartz that is colored purple with modifying hues of
blue or violet by trace amounts of iron is amethyst, so green
"amethyst" is a misnomer, as is its’ other nickname, lime "amethyst."
It is the same as referring to citrine as yellow “amethyst,” or
goshenite as white “emerald.” Unfortunately, though, the name is
catching on. I say “unfortunately” because we already have more than
enough confusing misnomers in the gem industry without another one. I
still get customers with their grandmother’s smoky “topaz” fairly
True amethyst occurs when trace amounts of iron atoms are present
along with the silicon and oxygen atoms that form quartz from the
rich solutions in geologic formations called pegmatites. Basically,
the color is caused by valence electron transfers between the
silicon, oxygen and iron atoms, as they “borrow” them from each other
to complete their requirements to “own” those ions (also called free
electrons). This causes a tiny bit of energy that causes the quartz
to absorb greens, oranges and yellows, while reflecting the blues and
reds that we see as purple. When amethyst is heated properly, these
ions’ circuit around the atom is relaxed, making it easier for them
to jump straight from the silicon atoms directly to the iron atoms,
avoiding the oxygen atoms altogether. That difference in energy
charge usually results in the change of absorption and reflection
that to our eyes appears yellow.
I’ve read that most of the green “amethyst” being produced comes
from the Brazilian Montezuma deposit, and a somewhat lesser amount
from Arizona. The same geologic events that create natural citrine
(local hot springs, magma intrusions, etc.) can likely also cause the
pale green prasiolite to occur naturally, as well. Just as the tone
and saturation of color in amethyst determines how intense the
yellow-to-orange color of citrine will be after heating, there are
similar factors involved as to why certain amethysts turn that pale
greenish color when subjected to the same treatment. Apparently, the
crystals from Montezuma lend well to becoming greenish.
Thanks for your concern, Karen. Accurate representation of gem
species and varieties are extremely important to all of us in the
industry, as you well know. Don’t get me started on the CZ/zircon
debate. They’re not even close.
James S. Duncan, G.G.
James in SoFL