About Gemstones

FOR DIAMOND GRADING … CLICK HERE. (coming soon!)

With so many gemstones to choose from, it is really helpful to know about their unique features when choosing one for your jewelry designs. Some gemstones are particularly suitable for certain methods of fabrication due to their hardness, variety of color or availability.  Here is a list of the most utilized gemstones on the market today.

Alexandrite:  Discovered in the 19th century and closely associated with the Russian Imperial family, which accounts for its name, Alexandrites’ most distinctive feature is its color-change.  Alexandrites change from emerald green to red and orange-yellow colors depending on whether they are viewed in artificial or natural light.  Commonly found only in small sizes, larger sizes (1 carat plus) with strong color change are a rare find.  Beware of simulants and synthetics – many stones claiming to be Alexandrites are often treated corundum/spinel or even glass.  Remember if something looks too good to be true, it probably is.

Apatite:  Well known for its electric neon blue color, Apatites can be green, yellow, and sometimes colorless in addition to blue.  Major sources of Apatites are Brazil, Burma and Mexico.  It rates a 5 on the Mohs scale of hardness and is therefore quite a soft gemstone not really suitable for rings.  However, Apatite earrings or necklace can be quite stunning due to its unique electric blue.

Aquamarine:  Often shortened to simply “aqua”, aquamarines are a variety of Beryl, as are emeralds.  Aquamarines are renown for its coloring which range from blue to blue green.  A usually very clean stone with few visible inclusions, it is a stone that wears well and is widely available.  A translucent variety is commonly known as “milky” aquas.  Aquas can also exhibit phenomenons such as cat’s eye and star when cut appropriately to accommodate the hollow tube inclusions distinctive to beryls – stones exhibiting such phenomenons are rare and are collector’s items.  Because aquamarines are found in large sizes (hundred of carats), the price per carat of aquas do not change after 1 carat – it is only the clarity and intensity of color that determines price of any stone larger than 1 carat.

Blue Topaz:  Blue Topaz is one of the most common gemstones on the market today.  Its color is that of a clear blue ranging from light to dark.  Trade names for the range in hue are Sky (light), Swiss (medium), and London (dark).  Natural Blue Topaz is quite rare and 99.9% of the Blue Topaz commercially available have been irradiated to achieve this color.  This is an accepted practice.  It is a very clean stone and is quite hard (an 8 on the Mohs scale) therefore, can be cut or carved into many different shapes and faceting styles.  Because of its perfect cleavage plane, if harshly impacted, Blue Topaz can break along the cleavage.

Coral:  Coral is an organic material.  It can be polished to a beautiful shine and shaped into many different forms such as beads or cabochons.  Sometimes they are left as branches in their natural state with some polishing to create a smooth shine.  Coral comes in a variety of colors, pale pink and salmon being the most popular.  However, Coral also naturally comes in white, black orange and red.  The most rare and valuable colors are a type of pale pink known as Angel Skin and red, described as “Oxblood.”  Beware of materials made from plastic, glass or porcelain passed off as Coral.  Genuine Coral will effervesce if acid is applied due to its chemical composition of sodium carbonate.  However, this is a destructive test.  Usually a close look at the material will suffice – since Coral is an organic material and is porous, imperfections will be present.  It is also softer than glass with a hardness of 3.5 on the Mohs scale, it should be stored carefully to avoid scratches.

Diamond:  A diamond is the hardest natural mineral on Earth and has one of the highest refractive indexes.  Because of those reasons, there are several distinctive properties belonging to diamonds:

1)  Diamonds have a high luster called “adamantine luster.”  Diamonds take on an almost metallic surface sheen when polished due to its hardness.

2)  Diamonds exhibit “dispersion”.  Rarely seen in any other gemstone, dispersion (also known as “fire”) are the flashing rainbow colors displayed when a diamond is rocked back and forth.

3)  A diamond is extremely brilliant.  Brilliance, often referred to as the internal luster of a gemstone, is the flash of light coming from within the gemstone.  This flash will fluctuate on and off when rocking the gemstone back and forth.  The more brilliant a gemstone is, the more valuable it is, in most cases.  Only transparent gemstones can exhibit this flash of light and the higher the refractive index of the gemstone, the more brilliant it will be.  The Cut of a diamond can affect its brilliance tremendously.

Note:  Contrary to what is commonly thought, diamonds naturally come in many different colors.  What gives diamonds its colors vary upon the color itself  i.e. yellow diamonds are colored by trace elements of nitrogen in the mostly carbon chemical composition.  Blue, trace elements of boron.  Many colors are currently still being studied.  One speculation of the cause of pink in diamonds is a distortion in the crystal structure rather than trace amounts of foreign elements.  Colorless diamonds are the most common and the larger certified diamonds are graded by GIA using a system beginning with the letter “D” (the most colorless) to “Z”.  Any stone beyond “Z” are called “fancy color”.  Fancy color diamonds are graded for their intensity and vividness of color.  Other factors that affect the value of a diamond in addition to color are carat weight, clarity, and cut – making up the ubiquitous 4C’s of diamond grading and value.

Emerald:  Belonging to the Beryl family, Emeralds are revered across cultures and history.  Traditionally, a deep bluish green color is considered the most desirable in Emeralds and these are often referred to as “Columbian.”  Because of the way Emeralds are formed, they are often included and a clean, intense vivid green Emerald can command prices to match that of diamond.  Inside this gemstone, one can often see what is called a “jardin” – inclusions that create the illusion of looking in a garden of green fauna.  A common treatment of Emeralds is to soak them in oil that has a similar refractive index as the stone itself to “fill” some of the inclusions thereby enhancing the clarity.  This is a common, impermanent and harmless practice.  One can even do this at home.  Emeralds are the softest of the precious gemstones – it is not a hard wearing stone – caution should be taken when worn.

Moonstone:  Moonstone is the trade name of the variety Feldspar belonging to the Orthoclase mineral species.  Feldspar is a very common mineral and takes up 60% of the Earth’s crust.  However, not all Feldspar are “Moonstones.”  In order to be considered a Moonstone, adularescence must be present.  Adularescence is the name given to the internal glow; a gem phenomenon similar to the glow of moonlight.  The most prized Moonstones are a clean, clear stone with intense blue adularescence.  Moonstones can also have base colors of white, peach, gray, brown, green, and yellow.

Garnet:  The most common and well known Garnet is a deep red color.  Until very recently, it was thought that Garnets come in almost every color except blue.  However, in the 1990’s, a blue garnet was discovered in Bekily, Madagascar and color-change garnets were also discovered in Kenya exhibiting the same color-change as the finest Alexandrites.  Another rare Garnet is the Demantoid Garnet which is a bright neon green with a high refractive index and displaying dispersion as a diamond.  In fact, the word “demantoid” roughly translates from the Dutch, meaning “diamond-like.”  A versatile gemstone with a hardness of 7.5 to 8, Garnets can be used in almost any type of jewelry and can be worn daily without too much worry.

Jade (Jadeite & Nephrite):  Jade is a general term used to describe two types of mineral, that of Nephrite and Jadeite.  In fact, there was no distinction between the two until the 19th century even though Jade had been in use in ornamental objects, drinking vessels and jewelry for thousands of years.  Jade comes in many colors such as yellow, white, lavender in additon to green.  The most prized color is a translucent intense apple green called Imperial Jade which can fetch millions of dollars at auction.  Thus far,  breaking a world record, an inscribed ‘Tai Shang Hunang Di’ white jade seal sold for $12.29 million. The previous world record for a jade seal was $5.9 million in 2007 at Sotheby’s Hong Kong.  Jade is an extremely prized gemstone throughout all of Asia.

Kunzite:  A lilac to pink variety of Spodumene named after the chief jeweler at Tiffany & Co. in 1902 by the name of George Frederick Kunz – also a noted mineralogist.  Kunzite is a very distinctive shade of pale lilac pink and is an attractive gemstone when a pink stone is desired.  Although it rates a 6.5 – 7  on the Mohs scale, it does have a cleavage so impacting the stone harshly will cause it to break along the cleavage plane.  For this reason, it is not recommended for setting into rings – pendants and earrings are fine.  Another point to be aware of about Kunzite is that it is a “nocturnal” stone.  Kunzites’ color will fade in sunlight.  This goes for heated or natural Kunzite although heated stones will fade at a faster rate.

Lapis Lazuli:  Lapis has been a prized gemstone since antiquity.  Trade in the stone is ancient enough for lapis jewelry to have been found at Predynastic Egyptian sites, and as lapis beads at neolithic burial sites. It is a relatively rare semi-precious stone and the best quality Lapis will have flecks of golden pyrite distributed throughout.  This stone is at its best in larger sizes, where its intense color and golden veins can really shine.

Malachite:  A vibrant green stone, Malachite takes its color from copper and large quantities have been mined in the Urals, Russia.  It is often used in decorative purposes, such as the Malachite Room in the Hermitage, which features a large Malachite vase.  The bright green color with banding or a mottled pattern is distinctive to Malachite and its particular shade of bright green is unmistakable.

Opal:  Opal is a made of microscopic silica spheres arranged in a cubic or hexagonal lattice structure.  The interference and refraction of light caused by these spheres are what causes the display of colors in precious opals.  Most precious opals come from Australia.  The most prized variety are black opals displaying harlequin play-of-color – an even distribution of bright red, blue, green, and violet.  A thin layer of precious opals are often backed by materials such as ironstone, obsidian, onyx, or basalt to make doublets.  By doing so, the backing provides strength and durability while also lowering the cost.  This is a common practice and is completely acceptable when disclosed.  Opals that do not display play-of-color are called common opals.  A bright orange variety coming from Mexico is called Mexican Fire Opal.

Quartz: (and its many varieties):

Agate:  A variety of Quartz, agates come in a large number of colors and can be translucent to opaque.  Some agates are solid in color while others are banded; still others have “eyes” (rings formed by banding).  Often used in hardstone carvings, agates have been in use since the ancient times – many intaglios and cameos were carved in agate i.e. carnelian.  Today, its versatility allows it to be used in a wide variety of jewelry designs and decorative items.

Amethyst:  A microcrystalline variety of Quartz, Amethysts have been used for thousands of years in jewelry and drinking vessels.  Its name derives from the Greek meaning “not drunken” … Amethysts were believed to have the power to stave off inebriation.  The most desirable color amethysts are called Siberian (regardless of its actual origin) and has a beautiful grape jelly color.  Always a shade of violet or purple, amethysts can range from being vivid and saturated to light and pastel depending on where they come from.

Citrine:  A form of Quartz (the most common mineral on Earth), Citrine has a distinctive hue.  It can range from pale yellow to yellowish orange sometimes having a red or brown tinge.  What gives Citrine its color is the oxidation of trace elements of iron present in its chemical composition.  Basically, as the iron particles inside the stone start to rust, the stone turns yellowish or orange-red.  Citrine and Amethyst are actually the same stone in different stages of iron oxidation.  Hence, it is very easy to turn an Amethyst into a Citrine by applying heat.  This is a common practice in the trade and most Citrines on the market have been heat treated to achieve its distinctive color.

Chalcedony:  A translucent to opaque variety of Quartz.  Chalcedony can come in a variety of colors, the most prized being an apple green variety named Chrysoprase.

Chrysoprase:  A variety of Chalceondy (Quartz), Chrysoprase is prized for its apple green color.  It is this color (not any markings or patterns) that make Chrysoprase desirable unlike other minerals in the same cryptocrystalline silica family.  The most beautiful Chrysoprase color is akin to Imperial Jadeite.  Used by the Greeks, Romans and Egyptians in jewelry and other ornamental objects, it is one of the most valuable Chalcedony gemstones.

Jasper:  A translucent to opaque variety of Chalcedony Quartz, Jaspers are extremely colorful stones.  The name literally means “spotted or speckled stone.”  Jasper has a wide variety of uses and can be found in decorative objects or cut into cabochons for jewelry.  Picture Jasper is a popular variety used in jewelry making because the colors preserved in the stone create “pictures” that often resemble mountains, sunsets or desert landscapes.  Highly popular with artisans and craft jewelers, Jaspers exude a natural quality that has wide appeal.

Onyx:  A black opaque variety of Quartz.  All onyx are dyed.  Onyx, as most people know it, does not exist in nature.

Tiger’s Eye:  An opaque variety of Quartz displaying banding in shades of caramel and chocolate.

Ruby:  The red variety of the gem species Corundum.  Ruby is one of the most prized gemstones in the world.  The best color is a fluorescent red known as “pigeon’s blood”.  Technically, a ruby must be a certain hue in order to be classified as a “ruby”.  However, some dark pink sapphires are called rubies depending on the leniency of the dealer.  Rubies have been interchangeable with red spinels until the 19th century.

Sapphire:  All other colors of the gem species Corundum except red.  Sapphires come in all colors of the rainbow from dark saturated colors to watery pastel colors.  The next hardest mineral to a diamond, sapphires are extremely versatile as they are durable and are available in many different colors, shapes, sizes, and qualities.

Spinel:  A gem species extremely similar to Corundum in both chemical composition and refractive properties.  There was virtually no distinction between sapphires and spinels until the 19th century when more advanced gem identification equipment became available.  Spinels come in a variety colors similar to sapphires.  They rate about the same as sapphires on the Mohs scale and therefore make excellent substitutes for sapphires although they are a beautiful gem in their own right.

Tanzanite:  A blue/purple variety of Zoisite discovered in Tanzania in 1967.  It is a rare gem as it is mostly only found near the foothills of Mt. Kilimanjaro in Tanzania.  Tanzanite comes out of the ground red/brown and heating is required to achieve its distinctive blue color.  Tanzanite is strongly trichroic meaning it displays blue, purple and a burgundy depending on crystal orientation.

Topaz:  Topaz is inherently colorless.  However, they can be “colored” by impurities in its chemical composition causing them to be yellow, brown, orange, or pink (rare).  Almost all blue topaz on the market is treated as this color is extremely rare in nature and is a result of natural radiation.

Turquoise:  Turquoise is an opaque blue to green gemstone.  The most noted samples are from Iran (what is referred to as Persian Turquoise).  American turquoise has more of a greenish tone to it and is often mottled with matrix.  Persian turquoise often exhibits the prized “robin’s egg” blue and is usually free of matrix.

Tourmaline:  Tourmaline is an extremely versatile gemstone due to the variety of colors it occurs in naturally.  The most common colors are a “bottle” green and a pink.  An extremely rare and prized variety known as Paraiba is a neon blue and comes from a locale by the same name in Brazil.  In fact, Brazil is the largest producer of any tourmaline.  Some tourmalines are naturally quite included (part of the beauty of the stone … like jardin in emeralds).  Tourmalines polish up to a high luster and is used in all forms of jewelry due to its wearability and durability.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s