February Birthstone: Amethyst

Amethyst was as expensive as ruby and emerald until the 19th Century, when Brazil’s large deposits were discovered. It was believed to prevent intoxication—amethystos means “not drunk” in ancient Greek. Today, as the most valued quartz variety, amethyst is in demand for designer pieces and mass-market jewelry alike, and its purple to pastel hues retain wide consumer appeal.

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Amethyst is the purple variety of the quartz mineral species. It’s the gem that’s most commonly associated with the color purple, even though there are other purple gems such as sapphire and tanzanite. Its purple color can be cool and bluish, or a reddish purple that’s sometimes referred to as “raspberry.”

Amethyst’s purple color can range from a light lilac to a deep, intense royal purple, and from brownish to vivid. Amethyst also commonly shows what is called color zoning, which in the case of amethyst usually consists of angular zones of darker to lighter color.

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Amethyst is the birthstone for February and the gem for the 6th and 17th wedding anniversaries.

https://www.gia.edu/amethyst

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January Birthstone: Garnet

Wide Variety of Garnets

Most people do not realize garnets come in a wide variety of gem types and colors, with many cutting options.
Garnets are a set of closely related minerals that form a group, resulting in gemstones in almost every color. Red garnets have a long history, but modern gem buyers can pick from a rich palette of garnet colors: greens, oranges, pinkish oranges, deeply saturated purplish reds, and even some blues.

Red garnet is one of the most common and widespread of gems, found in metamorphic rocks (which are rocks altered by heat and pressure) on every continent. But not all garnets are as abundant as the red ones. A green garnet, tsavorite, also occurs in metamorphic rocks, but it’s rarer because it needs unusual rock chemistries and special conditions to form.

Demantoid is a rare and famous green garnet, spessartine (also called spessarite) is an orange garnet, and rhodolite is a beautiful purple-red garnet. Garnets can even exhibit the color-change phenomenon similar to the rare gemstone alexandrite.

All garnets have essentially the same crystal structure, but they vary in chemical composition. There are more than twenty garnet categories, called species, but only five are commercially important as gems. Those five are pyrope, almandine (also called almandite), spessartine, grossular (grossularite), and andradite. A sixth, uvarovite, is a green garnet that usually occurs as crystals too small to cut. It’s sometimes set as clusters in jewelry. Many garnets are chemical mixtures of two or more garnet species.

Understanding Group, Species, and Variety Chart

Garnets are a group of closely related mineral species with many different color varieties.
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December Birthstone: Turquoise

Turquoise

18-karat Gold Collar with Turquoise Cabochon

This 18-karat gold collar, designed by Pierre Touraine, is set with a turquoise cabochon of fine texture and color. – Gift of Touraine Family Trust
Turquoise is found in only a few places on earth: dry and barren regions where acidic, copper-rich groundwater seeps downward and reacts with minerals that contain phosphorus and aluminum. The result of this sedimentary process is a porous, semitranslucent to opaque compound of hydrated copper and aluminum phosphate.
Turquoise is a prime example of an opaque colored stone that can be marketed both as a gem for jewelry and as an ornamental material.The Abdurreza Turquoise Mine

The Abdurreza turquoise mine lies in a dry, remote area of Iran.

Turquoise might lack the sparkle and clarity of transparent colored gemstones like ruby, emerald, and sapphire, but its multi-layered history and soul-satisfying color make it a desirable gem. Its color can range from dull greens to grass greens to a bright, medium-toned, sky blue. People value turquoise highly for its combination of ancient heritage and unforgettable color.

The traditional source for the top color, sometimes described as robin’s-egg blue or sky blue, is the Nishapur district of Iran, the country formerly known as Persia. So, quite often, you’ll hear people in the trade call turquoise of this beautiful color “Persian blue,” whether or not it was actually mined in Iran.

Top-quality turquoise has inspired designers to create elegant jewelry. It’s most often cut into cabochons, but it might also be cut into beads or flat pieces for inlays.

Although much turquoise jewelry is sleek and modern, many US consumers are familiar with the traditional jewelry of Native American peoples such as the Pueblo, Hopi, Zuni, and Navajo. People interested in Native American arts and crafts frequently collect this stylized silver jewelry.

Silver and Turquoise Squash Blossom Necklace

Elaborate silver and turquoise squash blossom necklaces like this are prized by collectors of Native American jewelry. – Courtesy Jaime Steelman

Turquoise is relatively soft, so it’s ideal for carving. Artists in Europe, Asia, the Middle East, and the Americas choose turquoise as a medium for carved jewelry and art objects. It’s often fashioned into talismans with Native American significance, such as bird and animal carvings, called fetishes.

Fetishes

Native American jewelry often features carved turquoise birds and animals, called fetishes. Courtesy Jaime Steelman.

Turquoise owes its texture to its structure and composition. It’s an aggregate of microscopic crystals that form a solid mass. If the crystals are packed closely together, the material is less porous, so it has a finer texture. Fine-textured turquoise has an attractive, waxy luster when it’s polished. Turquoise with a less-dense crystal structure has higher porosity and coarser texture, resulting in a dull luster when it’s polished.

Ornate Turquoise Vase

Turquoise is soft enough to be carved. This turquoise from China was crafted into an
ornate vase. – Courtesy Geological Museum, Beijing, China

Porosity and texture don’t just affect appearance: They also affect durability. Turquoise is fairly soft—it ranks 5 to 6 on the Mohs scale. Turquoise with a coarse texture might have poor toughness, too. Samples with finer texture have fair to good toughness.

Van Cleef & Arpels Ballerina Brooch and Matching Clip Earrings

This Van Cleef & Arpels ballerina brooch and matching clip earrings are designed with gold, diamonds, turquoise, and ruby. – © GIA & Tino Hammid, courtesy private collector

In turquoise, low porosity and fine texture are more valuable than high porosity and coarse texture. Coarse, porous stones are usually treated to make them smoother, shinier, and more marketable.

Sky-blue Turquoise

The smooth, waxy luster of these turquoise earrings results from closely grouped crystals that lessen porosity. – Courtesy GLEAM

Turquoise deposits usually form in iron-rich limonite or sandstone. Limonite creates dark brown markings in turquoise, while sandstone creates tan markings. These markings are remnants of the host rock within the turquoise, and can resemble splotches or veins. They’re called matrix.

Turquoise in its Host Rock

Turquoise is generally embedded in its host rock, like this specimen from Iran.

Manufacturers try to fashion turquoise so that no matrix is visible, but sometimes it’s unavoidable. Small amounts of turquoise might be scattered through the host rock in such a way that the rough material can’t yield any cut specimens large enough to fashion into gems without including some matrix.

Matrix in Turquoise

The matrix in spiderweb turquoise is attractively arranged in a network of thin lines.

The presence of matrix can lower the value of turquoise, but that doesn’t mean turquoise with matrix is worthless or unmarketable. Some buyers actually prefer the presence of matrix in fashioned turquoise if its effect is attractive and balanced.

This is especially true if it’s a type of turquoise known in the trade as spiderweb turquoise. It contains matrix in thin, delicate, web-like patterns across the face of the gemstone. The patterns provide a dark contrast to the gem’s bright blue.

In the market for top-quality turquoise, stones with no matrix at all command the highest prices. Gems with attractive spiderweb matrix rank second in value.

Courtesy of GIA  https://www.gia.edu/

Unique Topaz cuts

imperial topaz

Imperial is one of the most highly prized topaz colors, as seen in this spectacular prize-winning, orangy-red, flame-shaped gem. – Gem courtesy of John Dyer & Co.

TOPAZ RING; 12.25 CT; 1.48 TDW; 39000K; C5217A-001

This ring, designed by Maria Canale, holds a 12.25-carat untreated topaz from Brazil. The gem has no visible inclusions. – Courtesy Richard Krementz Gemstones

Blue Topaz Sculptural Gem (TM) 61.78 cts cut by John Dyer & Co.

This 61.78-carat carved topaz is a truly unique sculptural piece. Skilled workmanship intensifies the blue color to produce an effect like shimmering droplets of water. Blue topaz makes a perfect material for large carvings due to availability in large sizes. Lydia Dyer, Blue Topaz Sculptural Gem courtesy of John Dyer & Co.

November’s birthstone: Topaz

 

london blue topaz

Many consumers know topaz as simply an inexpensive blue gem. They’re surprised to learn that its blue color is hardly ever natural: It’s almost always caused by treatment. They might also be surprised to know that topaz has so many more colors to offer gem lovers, including pinks and purples that rival the finest fancy sapphires. Topaz 3

Topaz is allochromatic, which means that its color is caused by impurity elements or defects in its crystal structure rather than by an element of its basic chemical composition. The element chromium causes natural pink, red, and violet-to-purple colors in topaz. Imperfections at the atomic level in topaz crystal structure can cause yellow, brown, and blue color. Brown is a common topaz color, and the gem is sometimes mistakenly called “smoky quartz.” topaz 2

The color varieties are often identified simply by hue name—blue topaz, pink topaz, and so forth—but there are also a couple of special trade names. Imperial topaz is a medium reddish orange to orange-red. This is one of the gem’s most expensive colors. Sherry topaz—named after the sherry wine—is a yellowish brown or brownish yellow to orange. Stones in this color range are often called precious topaz to help distinguish them from the similarly colored but less expensive citrine and smoky quartz.

Topaz is also pleochroic, meaning that the gem can show different colors in different crystal directions.

topaz range