Abalone shell is a particularly prized type of mother-of-pearl, as it displays iridescence unmatched by any other mollusk. Its bold blues and greens give way to a rainbow of flashes of other colors to create a truly unique display.
Achroite refers to the colorless variety of tourmaline. An elbaite tourmaline variety, these gems are very rare and especially prized by collectors.
Generally transparent or translucent green, green-black, or grey-green in color, actinolite is named after the Greek word for "ray" or "beam," aktinos, referring to its fibrous nature. Actinolite also goes by the nickname 'ray stone' and is fairly prevalent worldwide.
Adamite is one of the most well known minerals in the specimen market although the mineral itself is not terribly common. Cut gemstones are rare because of its low hardness (3.5), brittle tenacity, and distinct cleavage. It is highly prized for its aesthetic crystal shapes and formations, bright color (often a yellow to greenish-yellow), and stunning fluorescence (bright lime green).
Adularia is a variety of feldspar found in hydrothermal veins in mountainous areas, from one of which it derives its name: the Adular Mountains of Switzerland. It commonly forms as colorless to white, cream, pale yellow to pink, or reddish-brown, glassy, prismatic, twinned crystals. These transparent to colorless gems often display a white to blue sheen.
Aegirine is a member of the pyroxene group along with jadeite. It is typically dark green to dark brown in color and crystals comonly have distinct terminations. It is rarely seen as a faceted gemstone, probably because it appears to be almost black due to its high saturation. It has good hardness at 6, and moderate to strong dispersion, when its saturation does not obscure it.
Aeschynite is an uncommon, rare earth mineral that is seldom cut into a gemstone. Two varieties of aeschynite also contain the elements cesium and thorium which are radioactive. It is not recommended to store this mineral in inhabited areas or to have prolonged exposure to the body.
Named after the country, Afghanistan, where it was first discovered in a lapis lazuli mine in 1968, this rare and complex aluminosilicate forms blue crystals ranging from light aquamarine shades to saturated sapphire blue hues. The scarcity of gem-quality afghanite makes it a true collector's stone.
Agate is the banded form of chalcedony, a cryptocrystalline variety of quartz. Rather than a single crystal, it is composed of a myriad of miniature crystals that can only be seen with extreme magnification. Agate's name is derived from the site of its discovery, the river Achates (now Dirillo) in southwest Sicily. You will often find striking curved or angular banded patterns of color flowing within agate, which are caused by the presence of various minerals, often iron and manganese. One of the oldest known gemstones, agate is a favored material of lapidaries and artisans around the world.
Akoya pearls tend to be the most consistently round and near-round pearls, which makes them perfect for matching for multi-pearl jewelry. Akoyas are saltwater pearls prized for their roundness, luster, and color. They are small, ranging from 2 to 11 millimeters, as the akoya oyster is the smallest pearl-producing oyster. Akoya pearls are considered the "classic" pearl with their generally white to cream color, having rose or silver overtones.
Alabaster is a fine-grained massive form of gypsum. Alabaster ranges from white to yellow, pink, and brown. Due to its porosity it is often dyed. It has been used for centuries for statues, carvings, and other ornamental purposes. Treated alabaster is used as a marble simulant. Due to its extreme softness, it is ideal for fashioning into works of art.
Alexandrite is the rare color-change variety of the mineral chrysoberyl. Its rarity is a result of its unlikely chemical makeup. Alexandrite displays the color change phenomenon because trace amounts of Cr3+ has substituted for Al3+ in the crystal lattice. This substation rarely takes place making alexandrite extraordinarily coveted.
Blue-green specimens of microline are called amazon stone or amazonite, named for its supposed discovery location near the Amazon River. Amazonite that is used in jewelry is generally cut into cabochons. Gem-quality amazonite is found in the Ilmen and Ural Mountains of Russia, the Pikes Peak district of Colorado and in Minas Gerais, Brazil.
Amber is the ancient fossilized resin of trees that grew in forests millions of years ago. Over the eons, chemical and physical changes occurred, fossilizing the resin to produce what we know today as amber. Research indicates that amber ranges from about two million to 360 million years in age, although most gem quality amber is between 10 million and 50 million years old. Hardened resin that is significantly younger than amber, is known as copal. Although the age boundary that differentiates amber from copal is still debated, copal is considered to be less than 10 million years old, with a large proportion being significantly younger.
Amblygonite is quite possibly one of the most beautiful pastel colored gemstones that you may have never heard about. It belongs to a class of minerals known as phosphates and forms a solid-solution series with montebrasite. Industrial grade amblygonite isn't that rare; however, when it comes to facet grade material, it quickly moves up on the hard-to-find list. Colors for amblygonite include pale yellow to greenish yellow and various shades of green to blue. On rare occasions, pink to light purple specimens may be found. Colorless material also is available.
If you are fortunate enough to be born in February, amethyst is your birthstone. This wonderful member of the quartz family often forms large, six-sided crystals. It's usually quite clear and can be cut into almost every shape, which makes it ideal for jewelry. Because amethyst is a 7 on the Mohs scale of hardness, it's very wearable. Versatile amethyst offers a wide variety of shades, from reddish to violet-purple. If you prefer soft, subdued colors, you will truly enjoy the pastel lavenders of amethyst. Are you drawn to deeper, richer colors? Then you should consider some of the intense purple amethyst from Africa or South America.
Ametrine is a bi-color quartz variety that, as its name suggests, is a unique combination of amethyst and citrine within a single crystal. How the gem forms is still a bit of a mystery, but the differences in color are believed to be the result of the presence of iron in different states of oxidation from natural heating. Combining the golden sunburst of citrine with the violet sunset of amethyst, this naturally colored gem is commercially mined at a single source: the remote Anah mine in Bolivia and is shrouded in fascinating local legends and lore.
Ammolite is a gem that comes from the fossilized shell of an extinct, squid-like creature called an ammonite. Found in Canada, the iridescent shell of fossilized ammonites is available as ammonite fossils or in iridescent gems cut from the fossils under the trade name ammolite. Ammolite's iridescent play of color is what makes it so distinctive and attractive. Its iridescence occurs when the fossilized ammonite shell becomes mineralized. Unlike most gems, whose colors come from light absorption, ammolite's iridescent color is caused by interference with the light that gets trapped within stacked layers of thin platelets that make up the fossilized shell. Since the layer of ammolite is typically thin, most ammolite is made into doublets or triplets for use in jewelry. A doublet is a thin slice of shell that is typically covered by a durable material (often crystal, glass or plastic) that both protect the gem and maximize its presentation. Triplets are typically assembled by placing a thin slice of shell between two layers of more durable material that are attached with epoxy. While shades of green and red are usually seen, all spectral colors are possible.
Ammonites were marine animals that existed during the Jurassic and Cretaceous periods, and are related to modern-day octopi, squid and cuttlefish. The same event that wiped out dinosaurs was the end of this species, as well. On rare occasions, the ammonite fossilized shells became mineralized, exhibiting a striking iridescent play of color. Ammonite is typically found as fossil specimens or as iridescent gems cut from the fossils under the trade name Ammolite.
Andalusite, an aluminum silicate, derives its name from the southern Spanish province of Andalusia, long believed to be the site of its original discovery. The actual locale was a different province in Spain, El Cardoso de la Sierra, but the name Andalusite endured. Andalusite's color play has been compared to alexandrite, but this is technically incorrect, as andalusite is trichroic rather than color changing. Andalusite displays different colors in different directions and features all its colors at once, whereas color change gems like alexandrite only change color when exposed to different light sources.