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Colored StonesBuyer's Guide » Stones & Metals In estate jewelry we are fortunate to see many exquisite colored stones. Many of the stones we see are of a quality that is difficult to find today. The most important aspect of a colored stone is of course color. To better describe a color, it can be divided into three component parts, hue, tone, and saturation. A stone's hue is its spectral color i.e. Blue, Red, Green, etc. A stone's tone is its relative lightness or darkness. Tone ranges from 1 to 8, with 1 being nearly colorless and 8 being almost black. The tones of most gemstones are between 2 (very light) and 7 (very dark). The last component, saturation, is the relative amount of color the stone has. Stones with high saturations have more vivid colors, while stones with lower saturations look more brown or gray. The higher the saturation the better! Clarity, while still important, is not nearly so as in diamonds. There are hundreds of different gem stones used in jewelry. The following is a list of the colored stones we most often deal with. Please click on a stone type to get more information about it. Many thanks to the GIA Gem Reference Guide for specific stone information.
Alexandrite (Chrysoberyl)Appearance : Alexandrite is a color-changing variety of chrysoberyl, and is usually transparent. Color in daylight ranges from yellow to brown to bluish-green. Color in incandescent light is usually orangey-red to reddish-purple. Tone is light to medium. Usually faceted. Hardness and durability : Chrysoberyl has a hardness of 8.5. Toughness (resistance to chipping and cracking) is excellent. What to look for: Alexandrites are the rarest of the colored stones and highly sought after. They are usually small stones, rarely exceeding two carats. Stones may change color completely, or only
slightly. The greater the degree of color change, the more valuable the stone. Beware: synthetic alexandrite, and a synthetic color-changing sapphire sold as alexandrite are very common in the marketplace,
and should always be disclosed. Amethyst (Quartz)Appearance : Reddish-purple to bluish-purple variety of quartz, usually transparent. Usually faceted. Hardness and durability : Quartz has a hardness of 7. Stones with a hardness of 7 or lower are more prone to surface scratches. Application of high heat may change stone color. Prolonged exposure to light may cause some stones to fade. What to look for: Amethyst should be a medium to medium-dark tone with a strong saturation of color. Because of amethyst's relative abundance, large inclusion-free stones are readily available.
Aquamarine (Beryl)Appearance : A greenish-blue to blue variety of beryl, Aquamarine usually has a light to medium light tone. Usually transparent. May be faceted or cut en cabochon. Hardness and durability : Beryl has a hardness of 7.5 to 8. High heat may cause fractures if liquid inclusions are present. What to look for: A blue hue is generally preferred to greenish blue. Stones should be free of eye visible inclusions and have a strong saturation of color. Stronger blues are much more valuable
then pale colors. Almost all aquamarine is heat treated to improve its color. Cat's Eye (Chrysoberyl)Appearance : Yellow to yellowish-brown to yellowish-green variety of chrysoberyl, usually semitransparent to semitranslucent and exhibiting chatoyancy (cat's eye effect). Cat's Eye chrysoberyl is always cut en cabochon to show the eye. Hardness and durability : Chrysoberyl has a hardness of 8.5. Toughness (resistance to chipping and cracking) is good to excellent. What to look for: Stone should be cut to show a nice, clean, and centered cat's eye. A honey colored yellow, which produces a "milk and honey" combination with the cat's eye is the preferred
color. Chalcedony (Quartz)Appearance : Chalcedony is the microcrystalline variety of quartz, i.e. many tiny crystals of quartz grown together (Amethyst and citrine are single, large crystals). It can be any color and is usually semitransparent to opaque. It may be cut en cabochon, as a tablet, or carved (sometimes into cameos). Hardness and durability : Chalcedony has a hardness of 6.5 to 7. Stones with a hardness of 7 or lower are more prone to surface scratches. Prolonged exposure to heat may change color. What to look for: Chalcedony comes in myriad varieties. Chalcedony varieties we usually deal with include the following: Agate is chalcedony with curved or angular bands or layers. Bloodstone is dark green with small spots or red or brown. Carnelian is the orangey-red to brownish-red variety of chalcedony.
Chrysoprase is a medium green and appears similar to fine green jade. Onyx is chalcedony composed of straight parallel layers of different colors. Sard is similar to carnelian but
darker and with a more brown color. Citrine (Quartz)Appearance : Yellow to orange to brownish-orange variety of quartz, usually transparent. Usually faceted. Hardness and durability : Quartz has a hardness of 7. Stones with a hardness of 7 or lower are more prone to surface scratches. Stones may change color when exposed to high heat. What to look for: Citrines should be free of eye-visible inclusions are have nice strong color. Orange is the preferred hue, with a medium-light to medium tone. Emerald (Beryl)Appearance : The green to bluish-green variety of beryl, usually translucent (heavily included) to transparent. Tone can vary from light to very dark. Emeralds are almost always included (often called the "garden"). May be faceted or cut en cabochon. Hardness and durability : Beryl has a hardness of 7.5 to 8. Emeralds are prone to chipping and cracking when heated or struck. Stones with more and larger inclusions are more fragile than less included stones. Care must be exercised when wearing emeralds on a daily basis, especially in rings. What to look for: Emeralds should have a nice deep green to bluish-green color. Fine stones often seem to glow from within. Inclusions are acceptable, but should be subtle and not detract from the
stone's beauty. Oiling an emerald to improve its clarity is considered an acceptable treatment and is often done as soon as the rough stone is extracted from the mine. Dianne's does not knowingly sell
emeralds with any other type of enhancement (such as fracture filling). GarnetAppearance : Garnets are a large group of gemstones with a similar chemical composition. Although most famous for their deep red, garnets come in every color with the exception of blue and are usually transparent. May be faceted or cut en cabochon. Hardness and durability : Garnets have a hardness of 6.5 to 7.5 depending on type. Abrupt changes in temperature may cause fracturing. What to look for: Garnet comes in many varieties. Garnet varieties we usually deal with include the following: Almandite or Almandine (Reddish-orange to red), Demantoid (Yellowish-green to green with high dispersion), Hessonite (Yellow-orange to reddish-orange), Pyrope (Reddish-orange to deep red), Rhodolite (Pink to reddish-purple), Spessartite (Yellowish-orange to reddish-orange), Tsavorite (Yellowish-green to deep green). Because of the wide variation in color and tone of the different garnets, a general guideline is to go with the most eye-pleasing color. Stones should have a strong saturation of color, light, medium,
or dark tone, and be free of eye visible inclusions. Brownish stones are the least valuable. Heliodor (Beryl)Appearance : The greenish-yellow to orangy or yellowish-brown variety of beryl, usually transparent. Also called "Sun Stone". Heliodor is usually faceted. Hardness and durability : Beryl has a hardness of 7.5 to 8. High heat may cause fractures if liquid inclusions are present, and cause color to change to pink. What to look for: Heliodor, like aquamarine, is usually light in tone. Look for a light, but bright yellow with just a hint of green. Stones should be free of eye-visible inclusions. JadeAppearance : Between the two types of Jade, Jadeite and Nephrite, almost every color is available. Colors are often mixed and mottled in jade pieces. Jade can range from semi-translucent to translucent, with the rarest and most expensive type being Imperial Jade, which is nearly transparent and resembles an emerald. Jade used in jewelry is usually cut en cabochon, but is sometimes carved. Hardness and durability : Jadeite Jade has a hardness of 6.5 - 7. Nephrite Jade has a hardness of 6 to 6.5. Jade is the toughest (resistance to chipping and cracking) stone in jewelry. What to look for: A strong, even color is the most desirable. The more translucent the stone, the more valuable. Beware: the majority of jade, especially inexpensive jade, is dyed. Dianne's
will not knowingly sell dyed jade. Kunzite (Spodumene)Appearance : Pink to bluish purple variety of spodumene, usually transparent and light in tone. Kunzite is usually faceted. Hardness and durability : Spodumene has a hardness of 6.5 to 7. Stones with a hardness of 7 or lower are more prone to surface scratches. Spodumene is prone to chipping and cracking when
struck and should be What to look for: Kunzite is usually very light in tone and pale in color. The more intense varieties of pink are the most prized. Stones are usually large and free of eye-visible inclusions.
Lapis LazuliAppearance : Lapis is usually slightly greenish-blue to violetish-blue with flecks of pyrite and white veins of calcite. Lapis is a rock as opposed most gems which are mineral crystals. It is composed primarily of three component minerals, lazurite (blue), pyrite (the yellow flecks), and calcite (the white veins). Lapis is usually cut en cabochon, or as a carving. Hardness and durability : Hardness varies from 5 to 6 depending on composition. Heat may enhance darkness of stone, or produce an undesirable green color. What to look for: Blue or violet-blue lapis is more valuable than the greenish-blue variety. Less pyrite and calcite is preferable, as is a nice even coloration. Moonstone (Feldspar)Appearance : Colorless to white variety of feldspar, exhibiting adularescence (moonstone effect), and usually transparent. Always cut en cabochon to show effect. Hardness and durability : Hardness of 6 to 6.5. High heat my cause cracking and/or cleavage (splitting). What to look for: Moonstone should have a nice, even glow that rolls across the stone as it moves and a neutral bodycolor. Morganite (Beryl)Appearance : Pinkish-orange to purplish-pink variety of beryl, usually light to medium light in tone and transparent. Named for the famous financier J.P. Morgan. Morganite is usually faceted. Hardness and durability : Beryl has a hardness of 7.5 to 8. High heat may cause fractures if liquid inclusions are present. What to look for: Morganite is similar to Kunzite in appearance. The richer, pure pinks are the most desirable. Morganite is usually free of eye-visible inclusions, and large stones are available.
Opal Appearance : Precious opal is any number of similar minerals composed of silicates and water. The common characteristic is the presence of play-of-color (often mistakenly called "fire").
This play-of-color is caused Hardness and durability : Hardness ranges from 5 to 6.5. Of the major gemstones, opal is the most fragile. Opal is extremely susceptible to fracturing and should be worn with care. Heat may cause opals to fracture and play-of-color to disappear. Because of this fragility, opal lends itself to many superstitions. What to look for: Opals are generally grouped into three categories: White opal has a white to light grey body color (body color refers to the stone itself NOT the play-of-color) and is translucent to transparent. Black opal has a dark grey to
black body color and is translucent to transparent. Black opals are the most prized variety because their play-of-color is most noticeable against their dark background. Large even patches of color are preferred to small uneven ones, and opals having
a red play-of-color are the most valuable. Pearl Appearance : Organic gemstones formed in the bodies of certain freshwater and saltwater mollusks, pearls are made up of fine crystalline layers of nacre which is composed primarily of calcium
carbonate, water, and conchiolin (an organic binder). Pearls can have virtually any bodycolor, but the most common are white, cream, and black. In addition to their Hardness and durability : Hardness and durability: Hardness ranges from 2.5 to 4.5 depending on type of pearl. Medium heat may cause pearls to dry out and fracture. High heat may cause pearls to burn, turn brown and fracture. What to look for: Pearls come in a many varieties. Almost all modern pearls are cultured, i.e. the mollusk is farmed and seeded by man to produce a pearl. Natural pearls are extremely rare, but occasionally seen in estate jewelry. Pearls varieties we usually deal with include the following: Akoya pearls are the Japanese cultured saltwater pearls made famous by Mikimoto. They are usually white to cream in color, have a pink overtone, and range in size from 3mm to 9mm. Black
pearls, sometimes called Tahitian pearls, are farmed in many places in the south Pacific (including Tahiti of course). They have a grey to black bodycolor and wide range of overtones including
green, pink, and blue. Sizes range from 5mm to 15mm. Oriental pearls are natural saltwater pearls from the Persian Gulf region. Size ranges from 2mm to 9mm. They are usually white to
cream in color, Pearls should be round, have an even bodycolor, be free of major surface blemishes, and have a pleasing overtone and/or orient. PeridotAppearance : Peridot is yellowish-green to greenish-yellow, light to medium in tone and translucent (in heavily included stones) to transparent. It is usually faceted. Hardness and durability : Peridot ranges from 6.5 to 7 in hardness. Stones with a hardness of 7 or lower are more prone to surface scratches. Rapid heating may cause fracturing. What to look for: The greener and less yellow peridot is more highly prized. Stones should be free of major inclusions (peridot-specific "lilipad" inclusions are sought after) but lightly
included stones are acceptable. Ruby (Corundum)Appearance : Ruby is the red to orangy-red to purplish-red variety of corundum, usually transparent to opaque. Rubies may be faceted, cut en cabochon, or carved depending on their quality. Some cabochons may exhibit a six-sided star. Hardness and durability : Corundum has a hardness of 9, second only to diamond. Rubies are very tough stones and resist chipping and fracturing well. What to look for: While the majority of rubies are a more pinkish-red color, the rarest and most valuable is the medium tone, vivid red variety also known as "pigeon's blood". Rubies may
be lighter or darker in tone, as long as they have a strong saturation of color. Rubies should be free of major inclusions, but lightly included stones are acceptable. Star rubies should have a centered,
easy to see, six-rayed star with definitive "legs". Sapphire (Corundum)Appearance : Sapphires, often thought of as blue, are actually any color of corundum other than red (ruby). Stones may be opaque to translucent. Sapphires may be faceted, cut en cabochon, or carved depending on their quality. Some cabochons may exhibit a six-sided star. Hardness and durability : Corundum has a hardness of 9, second only to diamond. Sapphires are very tough stones and resist chipping and fracturing well. What to look for: Blue sapphires should be medium-light to medium-dark tone and a strong, royal blue. Golden sapphires should be a light to medium tone and yellow to orange in hue.
Padparadscha sapphires should be a light to medium tone with a pinkish-orange to orangy-pink hue. Pink sapphires should be light to medium in tone, and pink to purply-pink in hue.
Sapphires should be free of major inclusions, but lightly included stones are acceptable. Star sapphires should have a centered, easy to see, six-rayed star with definitive "legs". SpinelAppearance : Spinel can be any color and are often mistaken for other gemstones with similar colors. Stones can be opaque to transparent. Spinel may be faceted or cut en cabochon. Hardness and durability : Spinel has a hardness of 8. Intense heat may cause lighter stones to fade. What to look for: Spinels come in a rainbow of hue, tone, and saturation combinations. Fine colors are medium-light to medium-dark tone and have a strong saturation. Spinel should be free of major
inclusions, but lightly included stones are acceptable. Tanzanite (Zoisite)Appearance : Blue to violet to bluish-purple variety of zoisite, usually transparent. Tanzanite is usually faceted. Hardness and durability : Hardness ranges from 6 to 7. Stones with a hardness of 7 or lower are more prone to surface scratches. What to look for: Most tanzanite on the market is the lower quality grayish-blue (low saturation) variety. The most valuable is the intense blue to violetish-blue with a medium to medium-dark tone,
and strong saturation. Stones should be free of eye-visible inclusions. Virtually all tanzanite is heat reated to enhance its color. TopazAppearance : Topaz is usually transparent and comes in a variety of colors including: colorless, yellow, orange, brown, pink to red to purplish-red, blue, and green. It is usually faceted. Hardness and durability : Topaz has a hardness of 8. Topaz crystals have perfect cleavage in one direction, and are therefore susceptible to cleaving (splitting) even with a light blow to the stone. Strong heat may alter or destroy color. What to look for: Yellow to orange, and especially pinkish-orange (Imperial Topaz) are the preferred hues. Fine colors are medium-light to medium-dark tone and have a strong saturation. Topaz
should be free of eye-visible inclusions. Virtually all blue topaz is irradiated and heat treated to induce its color. Beware: Owing to their similar colors, many citrines are sold as topaz. Fine
orange topaz is much more valuable than fine orange citrine. TourmalineAppearance : Tourmaline can be any color, occasionally several colors in the same stone, and is opaque to transparent. Noteworthy colors are red (often called rubellite), blue (often called indicolite), green (often called chrome tourmaline), and watermelon (green outer crystal and red to pink inner crystal). Tourmaline may be faceted, cut en cabochon, or carved. Hardness and durability : Hardness ranges from 7 to 7.5. Strong heat may alter color. Sudden temperature changes may cause fracturing. What to look for: Tourmaline comes in a rainbow of hue, tone, and saturation combinations. Fine colors are light to medium-dark in tone and have a strong saturation. Red tourmaline (rubellite) may
be heavily included. Green (chrome) tourmaline should be free of eye-visible inclusions. All other colors should be free of major inclusions, but lightly included stones are acceptable. TurquoiseAppearance : Turquoise is an opaque, porous mineral, blue to bluish-green to green in color; often mottled and may show dark veins of matrix. Turquoise is usually cut en cabochon, carved, or fashioned into beads. Hardness and durability : Hardness ranges from 5 to 6 depending on material. Lower quality, more porous or chalky pieces may break apart more easily. Perspiration and cosmetics may cause discoloration. What to look for: American or Mexican turquoise can be green to blue with notable matrix, and is somewhat porous. The most valuable turquoise, often called "Persian" turquoise is an intense,
medium blue with low porosity ZirconAppearance : Zircon is usually transparent and comes in a variety of colors including: colorless, blue, yellow, green, brown, orange, red, and purple. It is usually faceted. Hardness and durability : Hardness ranges from 6 to 7.5. Stones with a hardness of 7 or lower are more prone to surface scratches. Heat may alter color. What to look for: Zircon has very high dispersion and will sparkle like crazy if well cut. Blue zircons (also called starlights) are the most prized and should be a medium-light to medium tone. Blue
and colorless zircons are almost always heat treated. |
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