Geoscience Reference
In-Depth Information
Table 11-4.
Main pearl-producing mollusks, water chemistry, geographic locations, typical pearl sizes and colors.
Adapted from Gemological Institute of America (2000), Matlins (2006) and Wise (2006).
Water
Type
Location
Size
Color
Salt
Pinctada fucata
“akoya” pearl oyster
Japan, China, Australia, South
Korea, New Guinea
6-7 mm
Gray, white,
yellow
Pinctada margaritifera
“black-lipped”
pearl oyster
Cook Islands, French Polynesia
south of equator, Hawaii
8-14 mm
Steel gray to black
Pinctada maxima
“silver- and
golden-lipped” pearl oyster
Indonesia, Malaysia, Vietnam,
Philippines, Thailand, Australia
8-15 mm
Cream, golden,
silver
Fresh
Cristaria plicata
“wrinkle” or “river”
shell
China, Vietnam, Japan, Korea
Most 3-5 mm
Up to 14 mm
Bronze, peach,
plum, champagne
Hyriopsis cumingi
“Unio” or “triangle”
shell
China
Megalonaias nervosa
“washboard”
shell
North America
White, cream
margaritifera
is commonly known as the pearl
mussel; it has a circumpolar distribution with a
lifespan that commonly exceeds a century
(Ziuganov et al. 2000; Helama and Valovirta
2008). In addition to modern pearls, ancient
pearls exist as a testament to wetland environ-
ments in the past; the oldest known fossil pearls
date from the Triassic, some 230-210 million
years old (American Museum of Natural History
2002).
Pearls are secretions that form within mol-
lusks in response to an irritant that enters the
shell and lodges in the mantle tissue. The
mineral composition of pearl and mother of
pearl is aragonite (CaCO
3
). When pearls form
within the mollusk, the surface skin is coated
in nacre, which consists of layers of aragonite
crystals joined by conchiolin, a binding protein
(Wise 2006). Nacre is added in concentric layers
that are microns-thin and resemble an onion
viewed in cross section. In the pearl-producing
mollusks, undulations in nacre layers produce
tiny grooves that act as a diffraction gradient to
break up light into component colors, which
create a rainbow or iridescence and a warm
glow that seems to radiate from inside (Fig.
11-11).
Early in the twentieth century, demand for
pearls exceeded the supply of natural pearls,
which had become scarce as a result of overi sh-
ing mollusks. At this time, a British biologist
working in Australia, William Saville-Kent, is
credited with creating the process used to
culture pearls (Matlins 2006). Two periculturists,
Tatsuhei Mise and Tokichi Nishikawa, applied
this technique and received a patent in 1907 for
the process of producing cultured akoya pearls
in Japan (Ward and Ward 1998). K. Mikimoto,
an entrepreneur, adapted the scientii c process,
using the Mise-Nishikawa method for commer-
cial production and made his name synonymous
with cultured round pearls sold to global con-
sumers. Japan dominated the pearl industry
with a half-century head start, but more recently
South Sea pearls are becoming a popular jewelry
choice, and 2011 was the i ftieth anniversary of
the French Polynesia-Tahitian cultured black-
pearl industry (
Jewellery News Asia
2011a).
Pearl production is a simple form of aqua-
culture with positive impacts on wetlands and
the economy. The production of South Sea
pearls serves to demonstrate the main proce-
dures as described by J. Branellec (2011, pers.
com.), a pearl farmer whose family helped initi-
ate cultured golden-pearl production in the Phil-
ippines. Culturing pearl starts with the capture
or harvest of wild
Pinctada maxima
mollusks,
which are needed to create a breeding stock.
This initial harvest was carried out by the
Badjao, an indigenous tribe from Malaysia but
mostly living a nomadic life on boats. After mol-
lusks reach a certain age of maturity, they are
separated into pearl hosts and donors. Donors
are chosen based on depth of gold, silver, or
black color in the shell; they provide the mantle
tissue that is grafted behind the bead nucleus
