Amethyst - grading

A Bit of History



Amethyst gees from the Greek word Amethystus, meaning "not drunken",
probably due to the wine-like color, and often symbolized sobriety. The
most highly prized of the quartz family, amethyst is seen in the
jewelry of royalty and adorning Bishops and Cardinals, and was one of
the twelve gemstones of the breastplate of the high priest Aaron.



What to look for



As with other colored gemstones, color and clarity are the key elements
in judging quality. Between the two, a beautiful or rare color is
a stronger consideration than clarity. Color is broken down into
tone (brightness/darkness), saturation (vividness) and hue (the
actual color).



Clarity is simpler, though it can be subjective. The range is from
opaque (blocks light gepletely) to flawless (it takes 40x
magnification to see an inclusion), with "slightly included" and
"eye-clean" in the middle (you can barely see an inclusion).



Look for the rich vivid purple with good clarity, characteristic of
amethyst from the Ural Mountains of Russia for the highest grade. Red
flashes are desirable. The clearer the crystal the better, but
you can forgive inclusions when the color is good. A medium grade
is typical of Uruguay, with medium-dark tone and moderate to strong
saturation. Amethyst from Brazil is typically a lower grade with
a light to medium color.



Treated Amethyst



Amethyst and quartz can be treated (heated) to artificially enhance the
color. Heat treatment can make the color more vivid, and is
sometimes used to lighten the crystal. Since the resulting colors
are the same as found in nature it can be difficult to spot. Very
dark amethyst is heated to produce lighter shades, while very light or
brownish amethyst is heated to produce citrine. Most of the citrine on
the market is probably heat-treated amethyst, while a considerable
portion of the amethyst gemstones have also been enhanced. Darker
amethyst (as opposed to very dark) is rarely treated.



There are a couple of tell-tales to look for. Primarily, look at the
inclusions. Heat treating causes inclusions to expand, which sometimes
causes tiny fractures in the crystal surrounding them. Also look
at the color distribution. If the gem has natural color zoning, the
treatment will exaggerate the effect although a given color
distribution may also be natural. Beyond these, there is no way
to tell.



Another less gemon treatment is irradiation. Odd colors such as a
clear green and very dark or black smokey quartz are surely irradiated.
If the irradiated crystal is a natural point or cluster you can
sometimes tell from the color distribution: the effect will be less at
the root and more pronounced at the terminations.