Category Gemstones

Chatoyant Gems - The Cat's-Eye Phenomenon
Gemstones

Chatoyant Gems - The Cat's-Eye Phenomenon

What causes the bright line of reflected light that moves under the surface of a chatoyant gem? Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Cat's-Eye Chrysoberyl: Chrysoberyl is the gem that exhibits the finest "cat's-eye." When the name "cat's-eye" is used alone, it is understood that the speaker is referring to a cat's-eye chrysoberyl.

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Gemstones

Fire Agate

A phenomenal agate with iridescent red, yellow, orange and green flash. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Arizona Fire Agate: The botryoidal hemispheres in this cabochon are very small, with most less than one millimeter in diameter. This specimen measures 8 mm x 12 mm and weighs 1.
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Gemstones

Synthetic Opal

Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Synthetic Opal Color Samples: A sample card displaying a collection of synthetic opal cabochons of various colors. This collection clearly illustrates the abilities of a synthetic opal manufacturer. We sent a cabochon from one of these cards (OP70) to the Gemological Institute of America's lab for identification.
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Gemstones

Moonstone

Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Colored Moonstone: Moonstone can occur in several different colors. Shown here, clockwise from top left: white moonstone cabochon measuring 16 x 12 millimeters; peach moonstone cabochon measuring 12 x 10 millimeters; gray moonstone cabochon measuring 11 x 9 millimeters; green moonstone cabochon measuring 15 x 10 millimeters.
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Gemstones

Opalized Wood

Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Herringbone Sequoia: These cabochons were cut from an opalized wood known as Herringbone Sequoia. The rough was found in the Snake River / Hell's Canyon area by an old-time rockhound in the mid-1900s and was sold as part of his estate. It is uncertain if it was found on the Idaho or Oregon side of the canyon.
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Gemstones

Gem Silica

A bluish green to greenish blue chalcedony that obtains its color from copper. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Gem Silica Cabochon: A gemmy, vivid blue cabochon cut from natural, translucent gem silica from the Inspiration Mine, Gila County, Arizona. It is a 1.59 carat trillion measuring about 7.
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Gemstones

Ant Hill Garnet

Tiny ants mine some of the best garnets. :-) Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Faceted ant hill garnet: An "ant hill garnet" with spectacular body color from Garnet Ridge, near Dinnehotso, Apache County, Arizona. This stone is a 7.6 x 5.7 millimeter oval, weighing 1.02 carats. Ant hill garnets larger than one carat are unusual.
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Gemstones

Sonora Sunrise / Sonora Sunset

A rock of cuprite and chrysocolla that makes red sky over green landscape cabochons. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Sonora Sunrise Pendant: A beautiful pendant cut from Sonora Sunrise with a sterling silver bail. The color pattern in the pendant is a good example of the “red sky over green landscape” that earned “Sonora Sunrise” its name.
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Gemstones

Matrix Opal

An intimate mixture of precious opal and host rock. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Andamooka Treated Matrix Opal: The cabochon above is an example of a limestone matrix opal from the Andamooka area of Australia. Tiny occurrences of opal are distributed through a light-colored limestone host rock.
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Gemstones

Ethiopian Opal

"Welo opal" is named after the Wollo Province of northern Ethiopia. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Ethiopian opal: Striking play-of-color in a cabochon of Ethiopian opal. Domains of bright color in a translucent to transparent opal is commonly seen in Welo opal. Table of Contents The New Opal Heavyweight A Short History of Ethiopian Opal Welo "Precious Fire Opals" Hydrophane Opals Ethiopian Opal Treatments Dye Treatment Smoke Treatment Sugar/Acid Treatment What's the Future of Ethiopian Opals?
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Gemstones

Fire Opal

Translucent to transparent opal with a fiery background color of yellow, orange, or red. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Mexican Fire Opal: Cabochons cut from fire opal found in Mexico. They all have a bright red, orange or yellow background color. Mexican Fire Opal: Some beautiful fire opals from Mexico that have been cut into faceted gems.
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Gemstones

Birthstones

Gemstones for the Month of a Person's Birth Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Photo Month Birthstones(s) January Garnet February Amethyst March Aquamarine, Bloodstone April Diamond May Emerald June Cultured Pearl, Alexandrite, Moonstone July Ruby August Peridot, Spinel September Sapphire October Opal, Tourmaline November Citrine, Topaz December Blue Zircon, Tanzanite, Turquoise Image credits: Aquamarine: Copyright iStockphoto / dolphinphoto; Diamond: Copyright iStockphoto / MXW Stock; Emerald, Opal, and Topaz: Copyright iStockphoto / mikheewnik; Pearls: Copyright iStockphoto / barbaraaaa; Sapphire: Creative Commons photo by Montanabw; Turquoise: Copyright iStockphoto / IrisGD.
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Gemstones

Tanzanite

A popular blue gem that is only produced commercially in one small area of Tanzania. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Faceted blue tanzanite: This violetish blue tanzanite is an exceptional faceted oval weighing 8.14 carats and measuring 14.4 x 10.5 x 7.6 millimeters in size. On the basis of its color and clarity, it would be rated in the top 1% of all tanzanite ever produced.
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Gemstones

Gems from Space

A few rare gem materials are pieces of extraterrestrial objects or are a product of their impacts. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Moldavite: Moldavite (also called vltavin or Bouteille Stone) is an amorphous glassy material, a mineraloid, that is usually olive green in color. It is thought to have formed during an asteroid impact about 15 million years ago in central Europe.
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Gemstones

Sunstone

Also known as "aventurescent feldspar" because some specimens contain light-reflecting inclusions that produce a bright flash. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Oregon Sunstone as a faceted stone and a cabochon. The stone on the left is a 7 mm round cabochon with abundant copper platelets weighing 2.
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Gemstones

Emerald

The bright green gem of the beryl mineral family. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Emeralds from Colombia: Emeralds in a calcite and shale matrix from the Coscuez Mine, Muzo, Colombia. The well-formed crystal with an attractive bluish-green color is about 1.1 centimeters tall. Specimen and photo by Arkenstone / www.
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Gemstones

"K2 Granite," also known as "K2 Jasper"

An azurite granite found at the base of K2, the world's second-highest mountain. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist K2 granite: A piece of dry K2 Granite. A wet surface would increase the intensity of the blue azurite orbs. This piece is approximately 10 centimeters across, and the largest azurite orbs are about 1 centimeter across.
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Gemstones

Labradorite

The plagioclase feldspar with an iridescent play-of-color that is often used as a gemstone. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Labradorite: Photograph of labradorite gemstones exhibiting a beautiful labradorescent play of iridescent colors. Photo by Joanna-Palys copyright iStockphoto.
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Gemstones

North Carolina Gemstone Mining

Author: Hobart M. King, Ph.D., GIA Graduate Gemologist North Carolina Rubies: Photo of North Carolina ruby rough. Copyright by Peter Cristofono. Ruby, Sapphire, Emerald and More! Most people are surprised to hear that rubies, sapphires, and emeralds have been found in North Carolina. They are even more surprised when they learn that there are about a dozen locations in North Carolina where anyone can look for gemstones and keep anything that they find.
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Gemstones

Red Beryl

An extremely rare gemstone that receives its red color from trace amounts of manganese. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Red Beryl: Crystals of red beryl on matrix from the Violet Mine in the Wah Wah Mountains of Beaver County, Utah. Approximately 11 x 7 x 4 centimeters in size.
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Gemstones

Polka Dot Agate

A beautiful translucent blue to white agate with suspended dots of various colors. Author: Hobart M. King, Ph.D., GIA Graduate Gemologist Polka dot agate: Several cabochons of polka dot agate cut using material from the Priday Agate Beds of central Oregon. These cabs show only part of the color diversity of the dots and the various types of background material.
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