31 March 2019

DECEMBER BIRTHSTONES – ZIRCON  is a colorful gem with high refraction and fire that’s unfairly confused with cubic zirconia.
Mineral: Zircon;
Chemistry: ZrSiO4;
Color: Blue, red, yellow, orange, brown, green;
Birefringence: 0.000 to 0.059 (low to high);
Specific gravity: 3.90 to 4.73;
Mohs harness: 6 to 7.5 (low to high);
COLOR: The most valuable colors of zircon are blue, bright red, and green;
CLARITY: Zircon is often eye-clean. Gems with noticeable inclusions are less valuable;
CUT: To maximize its brilliance, zircon is most often cut in rounds and ovals;
CARAT WEIGHT: Zircon in fine quality is rare in large sizes. Zircon weighs more than most gems of like size;
DECEMBER BIRTHSTONES – TANZANITE Poised between lush blue, vibrant violet, and rich purple, exotic tanzanite is found in only one place on earth, near majestic Mount Kilimanjaro.
Mineral: Zoisite;
Chemistry: Ca2Al3(SiO4)3(OH);
Color: Violet blue to bluish violet to violet purple;
Refractive index: 1.691 to 1.700;
Birefringence: 0.008 to 0.013;
Specific gravity: 3.35;
Mohs harness: 6 to 7;
COLOR: Deep saturated violet blue or blue violet are the most valuable tanzanite colors. Paler hues are more commonly found;
CLARITY: Eye-visible inclusions decrease the value of tanzanite, particularly in lighter colored stones;
CUT: Tanzanite is available in a wide range of shapes but cushion and oval cuts are most common;
CARAT WEIGHT: Tanzanite color is less saturated in smaller sizes. Gems must be above five carats in size to have fine color;
DECEMBER BIRTHSTONES – TURQUOISE Azure sky, robin’s egg blue: Vivid shades of turquoise define the color that’s named after this gem.
Mineral: Turquoise;
Chemistry: CuAl6(PO4)4 (OH)8.5H2O;
Color: Blue to green;
Refractive index: 1.610 to 1.650;
Birefringence: Not detectable;
Specific gravity: 2.76 (+0.14, -0.36);
Mohs harness: 5 to 6;
COLOR: The even blue color of this cabochon would be called Persian blue in the trade;
CLARITY: These free-form turquoise cabochons show a typical matrix pattern;
CUT: Although turquoise is usually cut into beads and cabochons, it can also be carved;
CARAT WEIGHT: Cutters work around large areas of matrix to yield pieces of evenly colored turquoise~31.jpg

30 March 2019

NOVEMBER BIRTHSTONES – CITRINE  is the transparent, pale yellow to brownish orange variety of quartz. Citrine is rare in nature. In the days before modern gemology, its tawny color caused it to be confused with topaz. Today, its attractive color, plus the durability and affordability it shares with most other quartzes, makes it the top-selling yellow-to-orange gem. In the contemporary market, citrine’s most popular shade is an earthy, deep, brownish or reddish orange.
Mineral: Quartz;
Chemistry: SiO2;
Color: Yellow to orange to orangy red;
Refractive index: 1.544 to 1.553;
Specific gravity: 2.66 (+0.03/-0.02);
Mohs harness: 7;
COLOR: Vivid yellows, reddish oranges, and earth tones are popular with consumers;
CLARITY: Eye-visible inclusions are not common in citrine. If present, they decrease its value;
CUT: Citrine might be carved, custom-cut, or calibrated for jewelry use;
CARAT WEIGHT: Citrine is available in a wide range of sizes for setting into a variety of jewelry styles;
NOVEMBER BIRTHSTONES – TOPAZ Honey yellow. Fiery orange. Cyclamen pink. Icy blue. In warm or cool tones, topaz is a lustrous and brilliant gem. Topaz actually has an exceptionally wide color range that, besides brown, includes various tones and saturations of blue, green, yellow, orange, red, pink, and purple. Colorless topaz is plentiful, and is often treated to give it a blue color. Topaz is also pleochroic, meaning that the gem can show different colors in different crystal directions.
Mineral: Topaz;
Chemistry: Al2(F,OH)2SiO4;
Color: Yellow, orange, brown, pink to red to purple red, blue, light green and colorless;
Refractive index: 1.619 to 1.627;
Birefringence: 0.008 to 0.010;
Specific gravity: 3.53;
Mohs harness: 8;
COLOR: The most valued topaz colors are orangy red to red. Blue gems are widely available;
CLARITY: Topaz used in jewelry is typically eye clean with no visible inclusions;
CUT: Topaz crystals are usually columnar, and cut as oval or pear shapes to improve yield;
CARAT WEIGHT: Topaz often forms as large crystals. These can yield sizable cut gems~30.jpg

29 March 2019

OCTOBER BIRTHSTONES – TOURMALINE  have a wide variety of exciting colors with one of the widest color ranges of any gem. Tourmaline’s colors have many different causes. It’s generally agreed that traces of iron, and possibly titanium, induce green and blue colors. Manganese produces reds and pinks, and possibly yellows. Some pink and yellow tourmalines might owe their hues to color centers caused by radiation, which can be natural or laboratory-induced.
Mineral: Tourmaline;
Chemistry: Elbaite Na(Li1.5,Al1.5)Al6Si6O18(BO3)3(OH)4;
Dravite NaMg3Al6Si6O18(BO3)3(OH)4;
Liddicoatite Ca(Li2Al)Al6Si6O18(BO3)3(OH)3F;
Chromedravite NaMg3Cr6Si6O18(BO3)3(OH)4;
Color: All colors;
Refractive index: 1.624 to 1.644;
Birefringence: 0.018 to 0.040;
Specific gravity: 3.06 (+0.20, -0.06);
Mohs harness: 7 to 7.5;
COLOR: Tourmaline’s rainbow colors have a wide range of color intensity and tone;
CLARITY: Pink to red tourmaline often has more visible inclusions than green to blue varieties;
CUT: Tourmaline crystals are often long, leading cutters to cut slender finished stones;
CARAT WEIGHT: Tourmalines come in all shapes and sizes. The value change for size varies with the variety~29.jpg

28 March 2019

SEPTEMBER BIRTHSTONES – SAPPHIRE The name “sapphire” can also apply to any corundum that’s not ruby red, another corundum variety. Besides blue sapphire and ruby, the corundum family also includes so-called “fancy sapphires.” They come in violet, green, yellow, orange, pink, purple, and intermediate hues. Some stones exhibit the phenomenon known as color change, most often going from blue in daylight or fluorescent lighting to purple under incandescent light. Sapphires can even be gray, black, or brown.
Mineral: Corundum;
Chemistry: Al2O3;
Color: Every color but red;
Refractive index: 1.762 to 1.770;
Birefringence: 0.008 to 0.010;
Specific gravity: 4.00;
Mohs harness: 9;
COLOR: Sapphires come in a variety of colors. Preferred sapphires have strong to vivid color saturation, regardless of hue;
CLARITY: Blue sapphires typically have some inclusions, but they generally have better clarity than rubies;
CUT: Sapphire is often cut with a brilliant pattern on the crown and a step cut pattern on the pavilion;
CARAT WEIGHT: Blue sapphires range in size, and large blue sapphires are more readily available than large rubies~28.jpg

27 March 2019

AUGUST BIRTHSTONES – SPINEL The Black Prince’s Ruby. The Timur Ruby. For centuries, spinel, the great imposter, masqueraded as ruby in Europe’s crown jewels. Until recently, spinel was an underappreciated gem with little consumer recognition. Increasing demand for ruby alternatives rekindled appreciation for spinel’s rich red color and history. In ancient times, southeast Asia’s mines yielded exceptional large spinel crystals, which became the treasured property of kings and emperors, often passing through many hands as spoils of war.
Mineral: spinel;
Chemistry: MgAl2O4;
Color: red, orange, pink, purple, blue, black;
Refractive index: 1.718;
Birefringence: None;
Specific gravity: 3.60;
Mohs harness: 8;
COLOR: The most valued spinel colors are bright red, cobalt blue, and vivid pink and orange. Pale lavender is more affordable;
CLARITY: Spinel with no visible inclusions is preferred. The more prominent the inclusions, the less valuable the gem;
CUT: Spinel is most often cut in cushion and oval shapes. When properly proportioned it has excellent brilliance;
CARAT WEIGHT: Fine-color spinel is rare above five carats. Most fine-quality rough is cut to non-standard sizes to save weight;
AUGUST BIRTHSTONES – PERIDOT Found in lava, meteorites, and deep in the earth’s mantle, yellow-green peridot is the extreme gem. The ancient Egyptians mined peridot on the Red Sea island of Zabargad, the source for many large fine peridots in the world’s museums. The Egyptians called it the “gem of the sun.” Today this gem is still prized for its restful yellowish green hues and long history. Large strongly-colored, examples can be spectacular, and attractive smaller gems are available for jewelry at all price points.
Mineral: Olivine;
Chemistry: (MgFe)2SiO4;
Yellowish green;
Refractive index:
1.65 to 1.69;
0.035 to 0.038;
Specific gravity:
Mohs harness:
6.5 to 7;
Although the best peridot is a pure grass green, most peridot is yellowish-green;
Most fine peridot is eye clean. Tiny black spots might be visible with magnification;
Peridot is cut in a wide variety of styles, including ovals, emerald cuts, and cushions;
Large crystals of peridot have cut gems more than 50 carats in size~27.jpg

26 March 2019

JULY BIRTHSTONES – RUBY  is the most valuable variety of the corundum mineral species, which also includes sapphire. Rubies can command the highest per-carat price of any colored stone. This makes ruby one of the most important gems in the colored stone market. In its purest form, the mineral corundum is colorless. Trace elements that become part of the mineral’s crystal structure cause variations in its color. Chromium is the trace element that causes ruby’s red color.
Mineral: Corundum;
Chemistry: Al2O3;
Color: Red;
Refractive index: 1.762 to 1.770;
Birefringence: 0.008 to 0.010;
Specific gravity: 4.00 (+/- 0.05);
Mohs harness: 9;
COLOR: is the most significant factor affecting a ruby’s value: Fine gems are a pure, vibrant red to slightly purplish red;
CLARITY: If a ruby’s inclusions affect its transparency or brilliance they reduce the gem’s value significantly;
CUT: Rubies are commonly fashioned as mixed cuts, which have brilliant-cut crowns and step-cut pavilions;
CARAT WEIGHT: Fine-quality rubies over one carat are very rare and price goes up significantly as size increases~26.jpg

25 March 2019

JUNE BIRTHSTONES – ALEXANDRITE Green in sunlight. Red in lamplight. Color-changing alexandrite is nature’s magic trick. Often described by gem aficionados as “emerald by day, ruby by night,” alexandrite is the very rare color-change variety of the mineral chrysoberyl. Originally discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa, and Brazil, but fine material is exceptionally rare and valuable.
Mineral: Chrysoberyl;
Chemistry: BeAl2O4;
Color: Bluish green in daylight, purplish red in incandescent light;
Refractive index: 1.746 to 1.755;
Birefringence: 0.008 to 0.010;
Specific gravity: 3.73;
Mohs harness: 8.5;
COLOR: Fine alexandrite is green to bluish green in daylight and red to purplish red in incandescent light;
CLARITY: Good quality alexandrite has few inclusions. Rarely, needle-like inclusions create a cat’s-eye;
CUT: Alexandrite is most often available in mixed cuts. Its rarity means it is often cut to save weight;
CARAT WEIGHT: Most cut gems weigh less than one carat. Larger, higher-quality gems rise in price dramatically;
JUNE BIRTHSTONES – MOONSTONE A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water. Moonstone is a variety of the feldspar-group mineral orthoclase. During formation, orthoclase and albite separate into alternating layers. When light falls between these thin layers it is scattered producing the phenomenon called adularescence. Adularescence is the light that appears to billow across a gem. Other feldspar minerals can also show adularescence including labradorite and sanidine.
Mineral: Feldspar;
Chemistry: KAlSi3O8;
Color: Colorless to White, Gray, Green, Peach, Brown;
Refractive index: 1.518 to 1.526;
Birefringence: 0.05 to 0.008;
Specific gravity: 2.58;
Mohs harness: 6.0 to 6.5;
COLOR: The finest moonstone is a gem of glassy purity with a mobile, electric blue shimmer;
CLARITY: Characteristic inclusions include tiny tension cracks called centipedes;
CUT: As it displays moonstone’s phenomena to best advantage, cabochon is the common cut;
CARAT WEIGHT: Moonstone comes in a wide range of sizes and carat weights~25.jpg

24 March 2019

MAY BIRTHSTONES – EMERALD is the bluish green to green variety of beryl, a mineral species that includes aquamarine. Gem experts differ on the degree of green that makes one stone an emerald and another stone a less-expensive green beryl. Most gemologists, gemological laboratories, and colored stone dealers call a stone green beryl when its color is “too light” for it to be classified as emerald. Even among that group, however, there’s a difference of opinion about what’s considered “too light.”
Mineral: Beryl;
Chemistry: Be3Al2Si6O183;
Color: Vibrant green;
Refractive index: 1.577 to 1.583;
Birefringence: 0.005 to 0.009;
Specific gravity: 2.72;
Mohs harness: 7.5 to 8;
COLOR: The most desirable emerald colors are bluish green to pure green, with vivid color saturation;
CLARITY: In Emerald expect to see inclusions that dealers like to call an internal “jardin,” or garden;
CUT: Due to the crystal shape emeralds are commonly cut as rectangular step cuts called emerald cuts;
CARAT WEIGHT: Because its density is lower, a one-carat emerald will appear larger in size than a one-carat diamond~24

23 March 2019

APRIL BIRTHSTONES – DIAMOND are among nature’s most precious and beautiful creations.
Mineral: Diamond;
Chemistry: C;
Color: Colorless;
Refractive index: 2.42;
Birefringence: None;
Specific gravity: 3.52 (+/-0.01);
Mohs harness: 10;
COLOR: Clarity grades assess the number, size, relief, and position of inclusions and blemishes;
CLARITY: The less color, the higher the grade. Even the slightest hint can make a dramatic difference in value;
CUT: Cut (proportions, symmetry, and polish) is a measure of how a diamond’s facets interact with light;
CARAT WEIGHT: Rarity means larger diamonds of the same quality are worth more per carat~23.jpg

22 March 2019

MARCH BIRTHSTONES – AQUAMARINE  Named after seawater, aquamarine’s fresh watery hue is a cool plunge into a refreshing pool. Aquamarine’s name comes from the Latin for seawater and it was said to calm waves and keep sailors safe at sea. March’s birthstone was also thought to enhance the happiness of marriages. The best gems combine high clarity with limpid transparency and blue to slightly greenish blue hues. Like many beryls, aquamarine forms large crystals suitable for sizable fashioned gems and carvings.
Mineral: beryl;
Chemistry: Be3Al2Si6O18;
Color: greenish blue, light in tone;
Refractive index: 1.577 to 1.583;
Birefringence: 0.005 to 0.009;
Specific gravity: 2.72;
Mohs Hardness: 7.5 to 8.0;
COLOR: Aquamarine’s preferred color is a moderately strong dark blue to slightly greenish blue;
CLARITY: Most cut gems are eye-clean. Large examples are available without visible inclusions;
CUT: Because aquamarine’s color is light, cutting is important and well-cut gems show brilliance;
CARAT WEIGHT: Aquamarine crystals range from tiny to very large—some even up to 100 lbs~22.jpg