Gemological answers
Answers to your questions on irradiated blue topaz, pearls

December 15, 2007

Mary Johnson, a scientist and writer with a doctorate in mineralogy and crystallography, was formerly a manager of research and development at the Gemological Institute of America. Have questions? Send them to Johnson via nationaljeweler100@yahoo.com.

By Mary L. Johnson, Ph.D.

Question: How does irradiated topaz affect health? Is it prohibited to import irradiated topaz into the United States?
Answer: Radiation is all around us, and it is impossible to make anything completely radiation-free. Irradiated topaz can contain certain isotopes that are hazardous to human health. In most—but not all—cases, this radiation decreases to "safe" amounts within two years. Radiation damage can cause skin ulcers, cancer and cell death, and can lead to mandatory amputations or even death, but effects depend on the isotopes present and their amounts.

Artificial radiation (radiation induced by human activities) is regulated in the United States by the Nuclear Regulatory Commission (NRC). Among other things, its Web site states the following on irradiated gems in a regulations section titled "Exempt Concentration Use" (10 CFR 30.14): "The use of nuclear material to provide a desired effect, such as the coloration of gemstones or altering electrical properties in silicon chips or wafers, or for testing purposes, such as tracer flow studies in a refinery, may result in residual byproduct material in the final product. When the product is released to the public by an NRC licensee, it must not contain residual byproduct material above exempt concentration limits found in 10 CFR 30.70, Schedule A."

Check with the NRC (NRC.gov) for any other laws that prohibit or restrict selling blue topaz in the United States.

Question: What are the differences between pearl types?
Answer: Pearls are rounded structures formed by mollusks, and since there are more than 250,000 mollusk species in the world, many pearls are obscure. Most gem-quality pearls are nacreous, having iridescent layers of aragonite and conchiolin at the surface. These mainly come from bivalves, such as pearl oysters, although not all bivalves produce nacreous pearls.

Originally, river pearls were distinguished from saltwater pearls, but with pearl culturing in the 20th century, other divisions became more meaningful such as natural versus cultured; and bead-nucleated versus tissue-nucleated versus non-nucleated, or keshi, cultured pearls.

Now, cultured pearls are distinguished by color and origin, including Japanese akoyas, black Tahitian pearls, white, silver and golden South Sea pearls, etc. A few quite attractive natural and cultured pearls in bronze and gray come from Baja California in Mexico. Vast numbers of white, cream, pink and purple tissue-nucleated freshwater pearls come from China.

Some natural pearls come from gastropods (marine snails) and are not nacreous, but have "flame structures" instead. These include conch pearls and Melo pearls. Mollusks that produce non-nacreous "pearls" include quahogs, scallops and the giant clam Tridacna. However, strict interpretations do not allow these non-nacreous concretions to be called pearls.

Nacreous abalone pearls may be natural or cultured, although the cultured ones are usually half-pearls or "mabes." And that gets us into the next level of division, by shape and degree of completion. The most common pearl treatments change pearl colors, creating black or golden colors. Many inexpensive pearl strands have been dyed or irradiated to produce exotic colors.