January

Garnet. Garnets are among the few gemstones that are unenhanced, and they come in every color of the rainbow except blue. To prepare for the holiday selling season, check which colors you have in stock, and take note of where they’re displayed. Sometimes colored stones are grouped by color rather than by species or birthstone.

The traditional color, a brownish or purplish red, is called almandite. Most people think this is garnet’s only color. Not true. There are two greens—the emerald-color tsavorite from Kenya and Tanzania, and the somewhat peridot-color demantoid. (Check the demantoid for dispersive fire.) Historically, demantoid comes from Russia, but yours may come from newer finds in Arizona and Mexico as well as Nigeria.

The orangey-yellow spessartite from Nigeria and Brazil is a popular garnet. Reddish-purple rhodolite (which takes its name from the rhododendron flower) from Brazil, East Africa, Burma, etc., also has become popular, as has the darker Concord-grape-colored garnet from India.

February

Amethyst. Amethyst—purple quartz—typically comes from Brazil. Although it can be heated to an even purer purple, heated amethyst usually creates citrine (yellow).

Both citrine and amethyst are colored quartz and belong to the same family as rock crystal (as in crystal balls, not lead crystal, which is leaded glass).

The synthetic amethyst made in Russia can be pretty and often stumps the experts. Some say that 50% of the amethyst in jewelry stores is probably synthetic—and the jeweler doesn’t know it. Talk to your colored-stone buyer, and then talk to your supplier about the origin of your amethyst. And here’s a holiday selling tip: If you want to be patriotic, you can sell amethyst from Arizona—the quality is nice, and it’s readily available.

March

Aquamarine and Bloodstone. Most aquamarine comes from Brazil, Madagascar, Mozambique, Nigeria, and China. It’s usually heated to remove the touch of green that makes the stone look like seawater (which is how it got its name—”aqua” plus “marine”). Some aquas from Nigeria that are a darker pure blue are reported to be untreated, but it can’t be proven.

Bloodstone, another gemstone favored for men’s jewelry, is an opaque green quartz with red splotches.

April

Diamond. These gems can occur in any color of the rainbow—and the more color they have, the rarer they are. Red and green are the rarest, with blues and pinks a close third and fourth. More commonly seen in high-end jewelry are fancy yellows. Champagnes are relatively inexpensive compared with other colored diamonds. At the other end of the spectrum, colorless diamonds are rare, too.

Diamonds can be enhanced in a variety of ways. Inclusions can be removed by laser-drilling a tiny tube down to the crystal, burning it out, and bleaching the black areas with acid.

Color can be added to diamonds using high pressure and high temperature (HPHT) or irradiation. HPHT also can remove color, as in the Bellataire diamond. Fractures can be filled with a glass-like substance to mask their appearance, and such stones are called “clarity-enhanced.” Most synthetic diamonds are yellow but any color is possible.

May

Emerald. Colombian emeralds have been designated “the best,” because the finest color comes from Colombia. But the label “Colombian” doesn’t guarantee the best color. Fine-quality emeralds have been found in North Carolina, and they command a high price because they’re so rare.

Emeralds have lots of inclusions, so high clarity is not expected. Color is the most important feature. Emerald fissures are commonly filled, in a process called “oiling,” with an epoxy resin to mask their brightness. Some fillings are true oils, but these can leak or dry out, so ultrasonic cleaning is not recommended for emeralds.

June

Pearls. The most perfectly round pearls are typically Japanese cultured pearls. A mother-of-pearl bead is implanted into the oyster (also called a mussel or a mollusk, but not a clam), which coats the bead with a thin layer of nacre. (Mother-of-pearl is nacre that coats the inside of the shell.) Tahitian pearls also are bead nucleated.

Chinese freshwater cultured pearls typically have no bead, which means the whole pearl is nacre. The luster—or “shininess”—of these pearls is typically less than that of Japanese pearls, and they’re not as round as Japanese pearls. But the Chinese freshwaters have wonderful colors, unmatched by the Japanese, and are much less expensive. Also, it’s common practice to bleach the sub-nacreous layer of drilled Japanese round cultured pearls using hydrogen peroxide, making the pearls uniformly white.

Take care of all pearls, including Chinese freshwaters. Never wear pearls while swimming, since chlorine will destroy the nacre and dull the surface. Perfumes and perspiration can do the same. Store pearls separately, otherwise contact with other jewelry might scratch the nacre.

July

Ruby. Ruby is red corundum. The mineral comes in all colors, including colorless, but when they’re predominantly red, they’re called ruby. All others are called sapphire. Burmese ruby has a reputation similar to that of Colombian emerald. Burma (now called Myanmar) produces the finest red, but Burma rubies are not always the most expensive—again, look for the color. Clarity is slightly more important than it is with emerald.

Natural red Burma rubies are rare. Much of today’s Burma ruby is from Mong Hsu (pronounced mong-shoo). Almost all Mong Hsu ruby is heated at high temperature, which not only helps boost the color but also heals the fissures.

August

Peridot. Usually a tough sell, this sleepy yellowish-green gem is currently in fashion. Both “pear-a-dot” and “pear-a-doe” are accepted pronunciations, but the latter is more common. Most commercial peridot comes from Arizona, but most of the larger sizes originate in Pakistan and Burma. The green sand beaches of Hawaii are composed of small grains of peridot.

September

Sapphire. Blue sapphire is traditional, but any color of corundum except red will do for September’s birthstone. Most colors are enhanced by heat. Much of the sapphire in today’s jewelry stores comes from East Africa (including Madagascar) as well as Sri Lanka (Ceylon). Sapphire is hard and durable; in fact, you probably use sapphire when you file your nails—an emery board is cardboard covered in grains of sapphire. (Sales note: Don’t highlight that to customers—it’s a real mystique-killer.)

October

Tourmaline and Opal. Tourmalines come in many colors and combinations of colors. Most come from Brazil. Watermelon tourmaline, with its green outside and pink inside, is a favorite. Pinks and reds can be color-enhanced using slight irradiation. There are no health concerns with the treatment.

Opals come from Australia. They are found among ancient seabeds in thin layers, which is why they’re sometimes capped by rock crystal quartz and backed by black onyx. In such cases, the thin layer of opal is protected in a triplet—three pieces of gems. Black opal is not truly black, but dark blue or green.

Opals can be enhanced by soaking in sugar and then in acid, which turns the sugar black and gives the stone a speckled look.

November

Citrine and Topaz. Yellow is November’s color, even though topaz comes in a variety of hues. Citrine is usually heated amethyst, but this probably can’t be proved. Yellow topaz is typically natural color, but blue topaz (which isn’t a birthstone) is irradiated. Both are found in Brazil. While many people refer to yellow topaz as “Imperial,” gemologists will tell you there must be a predominance of red-orange color for the gem to fit the title.

December

Turquoise, Blue Zircon, and Lapis. Lapis is from Afghanistan and helped the Northern Alliance fight the Taliban … so buy lapis. Turquoise, even today’s so-called “Persian turquoise” bought in Iran and Afghanistan, is possibly from Arizona.

Inexpensive turquoise can be enhanced by wax, and there’s a new and difficult-to-identify enhancement that strengthens and evens out the blue color. Synthetic turquoise can fool those unfamiliar with the blue gem.

Usually set in sterling silver, inexpensive material can be discolored if it absorbs silver polish. The black spider-web matrix of Arizona turquoise is originally brown—it’s dyed with black shoe polish.

Blue zircon comes from Cambodia and is typically heat-treated. The process is permanent, so the gem won’t change color. (Selling point: Zircon is a natural gem and not related to cubic zirconia, a synthetic.)

Alternates. Some alternatives to traditional birthstones include astrological gems and gemstones for the days of the week. For information, consult George Kunz’s The Curious Lore of Precious Gems.

For information on gemstone enhancement, visit the American Gem Trade Association Web site at www.AGTA.org, or call (800) 972-1162.

Information on pricing colored gems is available from Gemworld International, publishers of The Guide, Northbrook, Ill.; (847) 564-0555.

And you can always contact the JCK gem desk at (610) 205-1107, or e-mail groskin@reedbusiness.com.