GO 340 Gemstones & Gemology
Golden South Sea Pearls and Gold-lipped
Pinctada Maxima, pearls obtained from
Jewelmer. Photo by S.W. and J.S. Aber, 7/2011.
Image by S.W. and J.S. Aber, 7/2011.
|Pearls have been valued for their natural beauty, no faceting or polishing required, for some 4000 years (The History of Pearls). The term pearl is generally only used for naturally occurring pearls, while all others are prefaced with the word imitation or cultured (Schumann, 2009, p. 264). Throughout the 20th century, the popularity of cultured pearls has increased in part because of a reduction of natural sources of pearls. Schumann attributed this to pollution and depletion of resources while demand for pearls has increased (p.259). Jewelmer is a golden South Sea pearl producer in the Philippines as a wonderful example of how the pearl farming industry protects the marine environment from pollution and illegal fishing practices, an environmental gem. Jewelmer pearl farmers must keep the mollusks healthy and created many worthwhile webpages explaining process and pearls of the world, http://www.jewelmer.com/pearl101_1.php; the nature of the pearl, http://www.jewelmer.com/pearl101_5.php; gypsies of the sea, http://www.jewelmer.com/pearl101_3.php; modern pearl farming, http://www.jewelmer.com/pearl101_2.php, all on their Pearl 101 resource webpage. In addition, credible information on pearl farming is found at the Pearl-Guide.com, http://www.pearl-guide.com/pearl-farms.shtml|
According to Schumann (2007), approximately 70% of all pearls are strung and worn as necklaces (p. 261). Standard lengths are choker to rope and can be viewed here, http://www.jewelmer.com/howtocare_2.php. |
Fresh-water pearl strand (top), salt-water pearls, and mother-of-pearl shells.
Photo by S.W. and J.S. Aber; photo date 7/2011.
The princess length necklace of multi-colored fresh-water pearls is Chinese and pearls produced by Hyriopsis cumingi.
The loose black pearls of various overtones are resting in the Black-lipped pearl oyster, Pinctada margaritifera.
The loose silver and gold pearls are on the Golden-lipped pearl oyster, Pinctada maxima.
The opera length necklace of white salt-water pearls is Japanese Akoya, produced by Akoya oyster, Pinctada fucata.
Pearl quality is determined according to shape, color, size, and luster. |
|A natural pearl is created by bivalve mollusks, primarily oysters, Ostreidae, but also freshwater mussels, and rarely by snails. These filter feeders suck in water and nutrients, along with an occasional silt or sand sized grain called an irritant. The irritant may stick to the mantle and the outer skin of the mantle, the epithelium. Parasites also bore into shells and the mollusk will react to this irritant as well. The animal then secrets nacre, which is what forms the shell as well as coats the irritant with a nonattached, rounded pearl sac. The layers encrust the irritant, which may lead to a single pearl or a wart-like growth on the inside of the shell, called a blister or shell pearl, under the trade name of mabe pearl. The layers of nacre, mother-of-pearl, are aragonite, calcium carbonate, and an organic horn type substance, conchiolin, that binds the microcrystalline aragonite around a natural or surgically implanted irritant.
The most popular colors are white, pinks, and creams, but pearl may also be silver, golden, blue, green, and black. The color varies with the type of mollusk, the water, and the color of the upper conchiolin layer. Treated pearls are colored peach, lavender, and other colors, while some are bleached to be even whiter. Even though the hardness is only 2.5-4.5, they are compact and difficult to crush.
Freshwater oyster showing cultured pearls.
Photographed in Shanghai, China. Image taken from
The Girl With a Pearl Earring by Johannes Vermeer
1665, is now housed in the Mauritshuis Museum
in The Hauge, The Netherlands.
|Pearls vary in size from a pin head to pigeon's egg size. Natural clam pearls can fill the palm of your hand (http://www.goldenpearls.biz/tridacna-maxima.htm) but they are not gem quality! In contrast, South Sea pearls are the largest pearls produced in the world. Historically, the largest natural pearl ever found for its time was named the Hope Pearl, is 2 inches (5 cm) long, 3.25-4.5 inches (6.5-11.25 cm) in circumference, and weighs 1,800 grains... 454 carats... about 90 grams. It was named for Henry Philip Hope, one of the owners, who insisted the name be kept as a condition of the sale of the gem (just as he did with the Hope Diamond). The Hope family was in the banking business in the 18th and 19th centuries. The pearl was acquired between 1800 and 1810, was baroque shape and was mounted as a pendant with a cap red enameled gold, ringed with diamonds, rubies and emeralds. A nice account and image of the Hope Pearl history is at http://www.internetstones.com/hope-pearl-natural-saltwater-baroque-pearl-henry-philip-hope.html where the fate of the gem after Hope's death in 1839:
...the "Hope Pearl" together with some of the other jewels of the collection, left it at the South Kensington Museum (later Victoria Albert Museum) for many years, until they were sold at an auction at Christie's London, in 1886. The pearl was purchased by Messrs. Garrard & Co. of London, at a price of ?9,000 (pounds). In the year 1913, the value of the pearl was appraised at $17,000. In 1975, the "Hope Pearl" resurfaced again and was purchased by H. E. Mohammed Mahdi Al-Tajir, ambassador of the UAE to Great Britain and France, at a price of $200,000. He added the famous and historic pearl to his collection of pearls.
While, the Hope Pearl was on display with its companion, the Hope Diamond, in the Gallery of the Janet Annenberg Hooker Hall of Geology, Gems and Minerals, Natural History Museum of the Smithsonian Institution in 2005, it moved
from October 25, 2007 to March 10, 2008, to a "special exhibition of pearls, known as "Perles, une histoire naturelle" (Pearls, a natural history), held at the National Museum of Natural History in Paris" (Hope Pearl). Today the Hope Pearl completed the journey and is again located in the South Kensington Museum in London, the British Museum of Natural History (Schumann, 1997, p. 230).
Genuine pearls form in nature, whereas cultivated pearls are natural (not imitations!) but produced with human assistance in implanting the irritant. Approximately 90% of the pearl trade today is cultured. Genuine sea pearls are produced by sea mollusks living in warm waters, water depth of about 50-65 feet (15-20 m), and are produced by nonedible varieties of mollusk. Genuine river pearls are not common because pollution has virtually eliminated the oyster habitats. Cultured seawater pearls go back to China, 13th century, and rounded freshwater pearls were first produced by Carl von Linnaeus about 1721.
10 year project for matched golden pearl
strand, personal communication from Jacques
Branellec, Pearl Farmer (2/2011). This pearl
is the Philipppine national gem!
The normal bead size is 0.24-0.27 inch or 6-7 mm and when the bead is greater than 0.35 inches or 9 mm, the oyster mortality rate is 80 percent (Schumann, 1997, p. 234). The mollusk are kept in plastic cages, suspended at 2-6 m (6.5-20 feet) underwater and hung from bamboo floats or ropes fixed to buoys. Yearly pearl growth is dependent upon the water temperature, but may be up to 0.3 to 1.5 mm in warm water and 0.09 mm in cooler water, such as in Japan. The farmed mollusk is in the water 3-4 years for a total layer thickness of 0.8-1.2 mm.
Cultured pearls are treated by bleaching, dyeing, and radiation (not permanent) to alter the color. Pearl imitations are plastic (conspicuously light) to glass (conspicuously heavy). The glass bead is dipped repeatedly in a solution of ground fish scales and the island of Mallorca, Spain, is well known for its imitation pearl industry. The Persian Gulf has been the source of fine natural saltwater pearls, as well as the Micronesian islands, Japan, Sri Lanka, Australia, and Mexico, to name a few. Japan is the source for a majority of cultured saltwater pearls. The cultured freshwater pearl industry is increasing with a variety of shapes and colors created, although the typical shape is like a puffy rice grain, and color, white. For more pearl information, history, and lore... visit CW Jewelers.
Image taken from
and tanakawho (2006).
Highly recommended reading:
Return to the Syllabus or choose another gemstone below.
This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail: email@example.com Thanks for visiting! Webpage created: November 15, 2000; last update: October 9, 2013.Copyright 1999-2013 Susan Ward Aber. All rights reserved.