Kyanite

With a range of blue hues in a single stone, kyanite is a fabulous gem for beautiful and unique jewelry.  Kyanite has a particularly unique and interesting property: it has two  different measures of hardness in the same crystal.  A gem’s hardness is defined as its resistance to scratching and is usually stated as a single number or small range; diamond is 10 on the Moh’s hardness scale, quartz is 7.  When you look at a kyanite crystal,  it may appear to have a grain like a piece of wood; the hardness can be 5-5 1/2 in the direction of the grain and 7 across it.

Kyanite is nKYSSN102_aamed from the Greek word for dark blue, kyanos, from which we get “cyan” as a shade of blue.  Most kyanite is blue, but it can also be white, gray, orange, yellow and green.  Although still not very common in jewelry, good quality blue and green material is used for beads and cut stones.

Kyanite crystals grow in long flat “blades”.  The gem can be translucent to opaque and the color is often very unevenly zoned over the crystal.  It is a metamorphic mineral with chemical formula Al2SiO5.   It is also a “polymorph”; one of three minerals with the same chemical formula but different crystal structure (the other two minerals are andalusite and sillimanite).

Kyanite  can be found in many locations around the world including Austria, Burma, Brazil, Cambodia, India, Kenya, Myanmar, Nepal, Russia, Serbia, Switzerland, Tanzania, the United States and Zimbabwe.  Besides jewelry, kyanite is used in the manufacture of porcelain, spark plugs and  electronics.

Kyanite is fairly durable, but KYGVE102_16_ahas perfect cleavage that can cause the stone to split with a single hard knock or blow. Don’t use ultrasonic cleaners, steamers, bleach or other harsh chemicals when cleaning kyanite; use water and a mild soap.

References:
Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York.
Gemological Institute of America, Gem Identification Lab Manual, 5/2012
http://www.gemselect.com/gem-info/kyanite/kyanite-info.php

Phenomenal! (Part 2 of 2)

Phenomenon:(noun) A special (optical) effect displayed by a gemstone when it interacts with light. Gems with beautiful optical effects are often more valuable.

Here’s a short description of types of phenomena recognized in gemology and the gems commonly associated with each.  A gem can have more than one phenomenon.

Iridescence: A rainbow display that is created when light is broken up into different colors like in a soap bubble or oil slick.
Gems: iris agate, fire agate

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Labradorescence in labradorite

Labradorescence: A broad flash of color caused by light interacting with a type of crystal growth called twinning.
Gems: labradorite

Orient:  A shimmer of iridescent rainbow colors on or just below a pearl’s surface.
Gems: pearl, mother-of-pearl

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Koroit boulder opal pendant

Play-of-Color: precious opal is made up of sub-microscopic spheres stacked in a grid-like pattern. As the light waves travel between the spheres, the waves diffract, or bend and break up into the colors of the rainbow, called spectral colors.
Gems: opal, fire opal

 

Last month I covered adularescence, asterism, aventurescence, chatoyancy and color change in part 1 of this blog.

Sources:
Gemological Institute of America, Gem Identification Lab Manual, 5/2012
http://4csblog.gia.edu/2014/phenomenal-gems
http://www.gia.edu/opal-description
http://gemologyproject.com/wiki/index.php?title=Sheen

Phenomenal! (Part 1 of 2)

Phenomenon:(noun) A special (optical) effect displayed by a gemstone when it interacts with light. Gems with beautiful optical effects are often more valuable.

Here’s a short description of types of phenomena recognized in gemology and the gems commonly associated with each.  A gem can have more than one phenomenon.

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Adularescence in rainbow moonstone

Adularescence: A milky, bluish-white glow caused by scattering of light related to the crystal growth pattern.
Gems: moonstone

Asterism (star gems): Crossing bands of reflected light in the gemstone create a four- or six-rayed star in the dome of a cabochon.
Gems: ruby, sapphire, garnet, spinel, diopside, beryl, quartz, moonstone, sunstone

Aventurescence: A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.
Gems: sunstone, aventurine, sheen obsidian

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Tiger’s eye

Chatoyancy (cat’s eye gems): A display of a band of light, like a cat’s eye. It is caused by the reflection of light from many parallel, needle-like inclusions inside a gem.
Gems: garnet, ruby, sapphire, chrysoberyl, tourmaline, beryl, tiger’s eye, quartz, moonstone, obsidian, and others.

Color-Change: Gem changes color when exposed to different types of light.
Gems: sapphire, garnet, alexandrite, spinel

Next month I’ll cover iridescence, labradorescence, orient and play of color in part 2 of this blog post.

Sources:
Gemological Institute of America, Gem Identification Lab Manual, 5/2012
http://4csblog.gia.edu/2014/phenomenal-gems
http://www.gia.edu/opal-description
http://gemologyproject.com/wiki/index.php?title=Sheen

Rhodochrosite, the Bacon of Gemstones

Seems like there’s been quite a bacon fad over the last year.  Well I’m sure you’ll be happy to hear that gemology has it’s own candidate for the bacon craze – rhodochrosite.

Rhodochrosite, MnCO3, is an ore of manganese.  It is a beautiful, but fairly soft (Moh’s hardness 3.5-4.0) mineral.  Most beads and cut stones show beautiful pink, brown, and white banding (described as the “bacon-strip effect”), and are opaque.  Although it is usually seen in jewelry cut as cabochons it can also be found as transparent pink to reddish faceted gems.  The banded material is also used in carvings. The name comes from the Greek rhodon -“rose” and chroma – “color.”

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Rhodochrosite and sterling silver necklace. Item RDSSN102

Rhodochrosite was initially described at a deposit in Romania in the early 1800s.  Rhombohedral crystals are mined in Colorado, where it is the state mineral.  Most of the banded rhodochrosite used in jewelry today comes from Argentina.

Rhodochrosite is a great gemstone for earrings and necklaces but generally too soft to safely wear in rings or bracelets that get heavy use.  It scratches easily so should be cleaned with a mild soap and water.

Sources:
Gemological Institute of America, Gem Identification Lab Manual, 5/2012
https://en.wikipedia.org/wiki/Rhodochrosite
http://webmineral.com/data/Rhodochrosite.shtml#.VgthxJfi2xk

Natural or Treated? Common Gemstone Treatments

Did you know that many gemstones are routinely treated (also called enhanced)?
These treatments are generally used to change or improve the color, clarity, or durability of a gem. Some gemstones are significantly more valuable if they are not treated, but treatments allow many more beautiful stones to be made available to consumers. It is important to understand treatments are not inherently “bad” but that legally,  they must be disclosed to the customer if they are not permanent, require special care, or if they affect the value of the stone.

Here are some of the most common gemstone treatments, why they are used, and a few examples of the gems that may be treated in this way.  Sometimes more than one treatment is used to achieve a desired result.

Process: Bleach
Why: Improve color
Examples: Pearls and jadeite jade are commonly bleached to remove undesirable coloring.

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PEGFN103_a Pearls are commonly bleached (top) and are often dyed or irradiated (bottom)

Process: Dye
Why: Change or improve color
Examples: Stones such as lapis lazuli may be dyed darker blue to improve their color. White stones such as howlite or pearls may be dyed to resemble other stones such as turquoise or just to provide fun options for jewelry design.

Process: Fracture filling with dyes, glass, oils, polymers or resins
Why: Improve clarity and/or color
Examples: Emeralds are commonly fracture-filled to improve their clarity.

Process: Heat
Why: Change or improve color
Examples: Sapphires and amber are commonly heated to improve clarity. Tanzanite changes from brown to blue when heated and amethyst can be turned yellow and is sometimes then sold as citrine.

Process: ––Irradiation
Why: Change or improve color
Examples: Some gray pearls have been irradiated.  Colorless topaz is both heated and irradiated to create blue gems.

–Process: Stabilization/Impregnation with plastic, polymers or wax
Why: Improve durability and appearance
Examples: Soft stones such as turquoise, lapis lazuli and rhodochrosite are commonly stabilized.

Other treatments not covered here include high pressure high temperature (hpht), surface coating and lattice diffusion. You can learn more about these as well as the treatments above by clicking the GIA link below.

Sources:
Code of Federal Regulations Part 23 – Guides for the Jewelry, Precious Metals, and Pewter Industries
Gemological Institute of America (GIA) – Gem Treatments

Peridot

Peridot, (Mg, Fe)2SiO4, is the gem quality version of the mineral olivine. It’s the gemstone for those born in August and for 15th wedding anniversaries.

Fossil Ammonite with peridot, cultured pearls, and gold-filled. Item FAGFN103 Background of natural olivene crystals.

Fossil Ammonite with peridot, cultured pearls, and gold-filled. Item FAGFN103
Background of natural olivine crystals.

Peridot comes in a relatively narrow range of colors compared to most gemstones. That’s because the color is due to the amount of iron in the mix and not due to chemical impurities or distortions of the crystal structure. The color range goes from yellowish greens through brownish greens. Peridot crystals tend to have consistent color throughout (contrast this with a gem like amethyst which often goes from colorless through various saturations of purple in the same crystal).

From a gemology perspective, one of the cool features of peridot can only be seen with a microscope; there are often little inclusions called “lily pads” that are very distinctive and help identify the gem.

Olivine is often found in iron-rich rocks and can be seen filling the nodules left when gas escapes from molten lava. Been to Hawaii? If you go again, look around when you see the blocky types of basalt (cooled lava) with lots of holes – you may spot some olivine! It has also been found in meteorites.

There is a major deposit of gem quality peridot on the San Carlos Apache reservation in Arizona. Other notable locations for peridot include China, Pakistan, Vietnam, Myanmar, Egypt, and Tanzania.

Peridot has hardness of 6.5 to 7 on the Mohs scale. It has fair to good toughness. Warm, soapy water is the best method for cleaning peridot. Ultrasonic and steam cleaners are not recommended.

Sources:
http://www.gia.edu/peridot
https://en.wikipedia.org/wiki/Peridot

Quartz – so many gems, so much confusion!

Quartz, chalcedony, agate, jasper … What’s the difference?

The quartz and chalcedony gems provide a wide range of beautiful colors and patterns with very good durability. Although they all have the same basic chemical formula, SiO2, different impurities and/or conditions when the minerals form create different end results.

First we’ll define two major groups based on crystal size: quartz and chalcedony (pronounced kal-sed-n-ee).

Quartz varieties have crystals that can be seen with an optical microscope (and sometimes with the naked eye).

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Amethyst (item AMSSN102)

Some quartz varieties commonly used in jewelry include:
Amethyst – purple
Ametrine – purple and yellow in the same stone
Citrine – yellow
Rock crystal – colorless
Rose quartz – pink
Smokey quartz – brown

Chalcedony varieties are cryptocrystalline which means that individual crystals cannot be seen, even with the use of an optical microscope.  Chalcedony gems are subdivided into two groups: agate and jasper.

Agate has angular or curved banding. 

Blue lace agate  (item BASSN101)

Blue lace agate
(item BASSN101)

Some agates used in jewelry include :
Blue Lace Agatelight blue bands in a lacy or wavy pattern
Botswana Agate banded with fine parallel lines of white, purple, or peach
Crazy Lace Agatetwisting and turning bands of various colors
Eye Agatebanded, concentric rings that are perfectly rounded
Fire Agate  –  Form of Agate or Chalcedony that is iridescent

Jasper is a “general variety term for opaque chalcedony of any color or combination of colors except solid black or specially named material” (GIA).

Mixed jasper necklace (Item JSGFN101) displayed on ocean jasper slab

Mixed jasper necklace (Item JSGFN101) displayed on ocean jasper slab

Examples of “specially named” varieties include:
Bloodstone – dark green with red spots
Carnelian – orange
Chrysoprase – apple green
Onyx – banded, black and white
Sardonyx – banded, brown/red and white

To add to the confusion, a number of gems don’t follow the naming conventions:
Moss agate – green inclusions, not banded
Onyx- banded, should be agate
Sardonyx – banded, should be agate

There are also many quartz minerals that are not beautiful or rare enough to be considered gems, such as chert and milky quartz.

With all these beautiful colors and patterns to choose from, there’s a quartz or chalcedony gemstone for everyone! Which is your favorite?

Information sources:
Gem Identification Lab Manual, Gemological Institute of America, 5/2012
http://www.minerals.net
http://www.wikipedia.org

Jade – Confused? Here’s Why:

I’m often asked if I make jade jewelry. The answer is yes… and no. That’s because there are two different gemstones that can correctly be called jade. They are similar in hardness and can sometimes be difficult to tell apart visually, but they are very different chemically. Both have been used for thousands of years for tools, decorative carvings and jewelry.

Things that ARE jade:

Nephrite Jade: chemical formula Ca2(Mg,Fe)5(OH)2. Nephrite is found in many countries including along the west coast of North America (sometimes called Canadian or B.C. jade) and also in Australia and New Zealand where it is often used for carved pendants. I’ve most commonly seen it in bright medium and dark greens to almost black but it can also be grayish or brown as well. Nephrite is generally more affordable than jadeite. Here’s an example of one of my recent pieces incorporating nephrite:

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Fossil orthoceras with nephrite jade (item FOSSN104)

Jadeite Jade:  chemical formula NaAlSi2O6. Jadeite is also found in the US and Canada, parts of Europe, and Myanmar. This is the jade that comes in colors including apple-green, white, and pale purple. It often has a mottled appearance. It is available as beads but tends to be very expensive.

Jadeite is commonly treated and has been categorized into 3 types based on this:
Type A – Natural, untreated, may have a surface coating of wax; “true” color.
Type B – Chemically bleached to remove impurities then impregnated with wax or polymers.
Type C – Dyed to enhance color; often chemically bleached and/or impregnated with wax or polymers.

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Aventurine and cultured pearl necklace (item PEGFN102)

Gems that can be confused with jade:
Aventurine: A quartz that gets its green color from inclusions of green chlorite mica. Aventurine is harder and significantly less expensive than either type of jade and has beautiful color. I often use it in my jewelry.

Unfortunately, some gemstones are given  trade names that are descriptive rather than accurate. Some trade names are intended to make a stone sound more expensive or desirable. Here are a few examples with their actual identity:
African Jade: grossular garnet
Australian Jade: chrysoprase
Malaysia Jade: dyed translucent quartz
Mountain Jade: dyed high-grade dolomite marble
New Jade: serpentine
Olive Jade: serpentine

Buyer beware – don’t pay jadeite prices for nephrite, aventurine, or any of the other stones I’ve listed above. Proper gemological testing can easily identify these gemstones.

For more information:
http://www.gia.edu/jade

Nephrite:
http://www.mindat.org/min-2881.html
http://www.gemdat.org/gem-2881.html

Jadeite:
http://www.gemdat.org/gem-2062.html
http://www.mindat.org/min-2062.html

Amethyst: Power to the Purple!

amethyst

Amethyst crystals, cut gem, and beads

February’s birthstone is amethyst, the purple variety of quartz.

Last month I told you about the many different colors of garnets, which are caused by differences in chemical formula. Pure quartz (chemical formula SiO2) is colorless (and is called “rock crystal” in the jewelry industry). The different colors of quartz* are caused by defects in the crystal structure rather than by a consistent change in the  chemical formula. This often causes different amounts of color within even a single crystal (“color zoning”). For amethyst, iron, and possibly aluminum, impurities are believed to cause the purple color.

Amethyst deposits are found all over the world; many of the large mineral specimens come from Brazil and Uruguay, but other sources for the gem include Russia, Czechoslovakia, Zambia, and the United States. It is not uncommon to find relatively large crystals which makes this a very affordable gem, even in large sizes.

Other facts – Amethyst:

  • is the gemstone for those celebrating their 6th or 17th wedding anniversary
  • was believed to prevent intoxication—amethystos means “not drunk” in ancient Greek
  • is sometimes found in combination with citrine and is then known as “ametrine”
  • when heated can change color to become a golden citrine
  • has a hardness of 7 on the Moh’s scale

*Other quartz gemstones include citrine (yellow), aventurine (green), rose quartz (pink), tigers eye (brown), smokey quartz (brown or gray) and chalcedony (which includes jaspers and agates).

Sources:

  • Gemological Institute of America, Gem Encyclopedia page on amethyst: click here.
  • Manual of Mineralogy, 20th Edition, Cornelis Klein and Cornelius S. Hurlbut, Jr., 1977.
  • GemSelect

Garnets are Red … Sometimes

January’s birthstone, garnet, is generally associated with the color red. But did you know garnets also come in orange, green, brown, and other colors?

Garnets are actually a group of gems with similar, but slightly differing chemical formulas.  The generic formula is A2B3(SiO4) where A is calcium, magnesium, iron or manganese (Ca, Mg, Fe, Mn) and B is aluminum, iron or chromium (Al, Fe,Cr). The different combinations of elements create the different species of garnet (listed below with their common colors). Color can be a very helpful diagnostic feature when identifying some (but not all) gems.  For instance, spessartine garnet must always have an orange color component.

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Almandine garnet collected at Gore Mountain in New York (left), spessartine garnet crystal (locality unknown, right)

  • Pyrope: medium to dark reddish orange, red through slightly purplish red to pale pink, colorless
  • Almandine: brownish orange to brownish red to purplish red
  • Spessartine: orange, brownish orange, yellowish orange, reddish orange, and red-orange
  • Grossular: medium to dark orange, medium to dark green to yellowish green, colorless
  • Andradite: yellow to slightly greenish yellow or brown, green through yellow-green
  • Uvarovite: light to dark green through yellow-green to brownish green
  • Hydrogrossular: pink, green, brownish pink, white, gray

Because of the range of chemical formulas possible, garnets may also be mixes of more than one species.  In addition, some species have subspecies (called varieties).  Some examples are Demantoid (a variety of Andradite) and Hessonite (a variety of Grossular)

Some garnets also display “phenomena” such as stars, cat’s eye, and color-change due to features of that stone that affect how light is reflected and/or transmitted.

Other facts – Garnet: 

  • is the gemstone for those celebrating their 2nd wedding anniversary
  • is used as an abrasive
  • has been used in jewelry since ancient times
  • can be found in all three major rock types: igneous, sedimentary and metamorphic
  • has a hardness of 6.5-7.5 on the Moh’s scale

and comes in colors to please almost everyone!

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Sources:

  • Gemological Institute of America, Gem Encyclopedia page on garnets: click here.
  • Gemological Institute of America, Gem Identification Lab Manual, 5/2012
  • Manual of Mineralogy, 20th Edition, Cornelis Klein and Cornelius S. Hurlbut, Jr., 1977.