Gemstones & Pearls: Gemology
The cause of uniform bands around some pearls remains a
More oddly shaped pearls than ever have made their way into
the market, including an interesting type with concentric circles
seemingly etched into their bodies. Once discarded as an unwanted
byproduct of pearl culturing, these so-called circle pearls have
established their own loyal following. They can be vastly cheaper
than rounder, smoother pearls, and they get double-takes because
each one is distinct. What are the oysters that give birth to
these pearls doing?
The oysters might be trying to rid themselves of unwanted
intrusions resulting from pearl culturing. "No one knows
100%," says Fred Ward, author of Pearls (Gem Book Publishers,
Bethesda, MD). "If the pearls are stuck in one position,
it's possible they may be spun in one direction by the oyster's
Karen Hurwitt, a senior gemologist at the Gemological Institute
of America, offers another opinion. "Lots of factors could
play a role," she says. "You must start from the concept
the oyster is alive and is being induced with mantle tissue that
is meant to lie flat. [Mantle tissue is deposited by pearl culturers
through an incision made in the oyster tissue.] Irregularities
in the mantle graft could cause the oyster to react in a way
that causes unusual formations during the pearl's growth."
The oyster secretes a coating called nacre to envelop the
inserted tissue and smooth any rough surfaces. In its attempt
to rid itself of the intrusion, it spins the growing pearl in
"Not all pearl-growing areas harvest pearls showing the
growth rings," says Ward. He points out that circle pearls
occur much more in natural black cultured Tahitian pearls than
in other South Sea pearls, for example. They also are seen quite
commonly in cultured Chinese mantle section freshwater pearls.
"The development of these rings may have something to
do with the fact Tahitian oysters, after being nucleated, have
a hole drilled in the shell and are hung on a rack in the water.
Hanging in place, the pearls tend to spin in only one direction,"
he says. "Conversely, other South Sea oysters are in baskets
that are rotated and flipped so the oyster is not always in the
John Koivula, GIA's chief gemologist, says drag lines can
sometimes be seen radiating from a blemish on the pearl's surface,
supporting the view at least some pearls spin in one direction
during their growth. Ward cautions there's no conclusive evidence
to support any one theory.
The marketing of circle pearls (which have been dubbed "circles
of love" in a promotion campaign for Tahitian pearls) is
moving into higher gear, thanks to record production worldwide.
If you're considering them for your store, remember these selling
- Though cultured, circle pearls have a natural look because
- They are available in larger sizes, up to 12mm.
- Prices even for larger pearls are reasonable.
They sell for just 10%-25% of the cost of comparably sized, rounder,
- Each pearl is unique and, therefore, a conversation piece.
- In natural black cultured pearls, rich iridescent colors
can occur around the ring structure.
by Robert Weldon, G.G.