HAPPY VALENTINES

 

Let's answer some of your questions.

Q: Since you know a lot about gemstones, I hope you can answer something that has me confused. I love Black Onyx, but when I select it on your, and other web sites, it shows that it is dyed. Is Black Onyx real or a dyed rock? Also, when I visited Texas last year, I bought a souvenir, Mexican donkey, made of “ONYX”, but this stone is a soft, banded, tan stone that looks nothing like my Black Onyx. Is this Onyx, too? As I said, I am confused.

Thanks for your newsletter. I hope you will answer my question. J.D.

A: I don’t want to confuse you, but BLACK ONYX is real, it is dyed, and your donkey is also ONYX. Let me explain.

BLACK ONYX is natural, gray chalcedony with an added black pigment. Believe it, or not, chalcedony is slightly porous and can absorb liquids. In the case of BLACK ONYX, gray chalcedony is placed in a vat of concentrated sugar or honey solution and the solution is absorbed into the stone. Then the sugar saturated, chalcedony is placed in heated sulfuric acid. If you remember high school chemistry, the acid reduces the sugar, in the chalcedony, to pure, black, carbon, producing BLACK ONYX. Pure, black carbon is one nature’s most stable pigments.

The art of coloring chalcedony started back in old Roman times and was perfected in Idar-Oberstein, Germany, almost 200 years ago. Idar-Oberstein is one of the most famous, and oldest, agate (chalcedony) and gem cutting centers in Europe. The Germans developed numerous processes to produce various pigmented colors in chalcedony. By using inorganic pigments they produced permanent colors. Where as, when organic colors and dyes are used, they tend to fade in sunlight.

Although the German processes are secret, here are a few chemicals that can produce pigmented colors in chalcedony:

BLUE ONYX (or agate), Iron is the pigment. A solution of yellow potassium Ferro-cyanide id absorbed, then the saturated chalcedony is boiled in hydrous iron sulphate.

 

 

GREEN ONYX (agate), Iron is the pigment. A chromium salt solution is
absorbed, then the saturated chalcedony is given a heat treatment.

RED ONYX (or agate), Iron oxide is the pigment. An iron nitrate solution is absorbed, then the saturated chalcedony is “fired” (heated)

CIBJO, an organization that sets standards in the jewelry industry, has stated, “chalcedony and banded agates which have received a permanent and irreversible color change through heat treatment or with an acid or corrosive” DO NOT have to have a label stating “treated” when sold or used in commercial purposes.

Your souvenir ONYX donkey is crafted from ONYX MARBLE. Unlike BLACK ONYX, which is achalcedony (Quartz family), ONYX MARBLE is a banded limestone formed with either calcite or aragonite. ONYX MARBLE should not be confused with chalcedony, and should never be called just ONYX.

And now back to our toughness chart
GEM NAME COLORS  HARDNESS TOUGHNESS NOTES 
PEARL  WHITE, & MANY 2.5-4.5  USUALLY GOOD BUT VARIABLE THIN NACRE MAY CHIP OR FRACTURE EASILLY.  AVOID HEAT & ACIDS.  MOST WHITES ARE BLEACHED.  MODERATE HEAT & STRONG LIGHT PROMOTE DEHYDRATION & CRACKING.  SOME DYE COLORS MAY FADE. . 
NATURAL PEARL       PRODUCED WITHOUT OUTSIDE HELP.  RARELY ROUND.  HISTORICALLY  FROM SEA AND FRESHWATER MOLUSKS.
CULTURED PEARLS       PRODUCED BY INSERTING A “SEED” INTO THE MOLLUSK.
  SALTWATER C.P.       PRODUCED BY INSERTING A SHELL OR SHAPED BEAD INTO  A   SALTWATER MOLLUSK & RAISED IN SALTWATER “FARMS”.  LAYERS OF   NACRE OVER CENTER BEAD.  HIGHEST  % OF ROUND PEARLS.
  FRESHWATER C.P.       PRODUCED BY INSERTING A PIECE OF TISSUE INTO THE MOLLUSK AND   RAISED IN FRESHWATER POND.  F.W.PEARL IS ALMOST SOLID NACRE.
  MABE PEARL       AKA: BLISTER PEARL.  PRODUCED BY ATTACHING A BEAD OR SHAPED OBJECT TO THE SHELL OF A MOLLUSK & ALLOW IT TO BE COVERED WITH WITH NACRE.  THE PEARL IS CUT FROM THE SHELL, FILLED, & BACKED.  .
PERIDOT   YW/GN, OLIVE, BN   6.5-7 FAIR-GOOD AKA: OLIVINE, CHRYSOLITE.  AVOID ACIDS & HEAT.  TENDS TO BURST  UNDER GREAT STRESS.  FACET EDGES CHIP EASILLY. CATS’-EYE AND  STAR PERIDOT ARE POSSIBLE AND RARE
PYRITE  BRASS/YW-GY/YW 6-6.5 FAIR-POOR   .AKA: “FOOLS’ GOLD”, WRONGLY CALLED MARCASITE. BRITTLE.
QUARTZ GROUP MOST COLORS 7 GOOD AVOID THERMAL SHOCK. BRITTLE.
ROCK CRYSTAL COLORLESS 7   CLEAR, CAN HAVE CHEVRONS & OTHER INTERNAL PATTERNS.
SMOKEY QUARTZ  BROWN-BLACK,SMOKEY GREY     AKA: MORION & CAIRNGORM.  CALLED “SMOKEY TOPAZ”. HEAT FADES .
AMETHYST  VIOLET     AVOID STRONG LIGHT (FADES) & HEAT (FADES, &/OR BECOMES CITRINE.
CITRINE LT-DK/YELLOW,RED/BROWN     HEAT FADES
AMETRINE VIOLET & YELLOW     MIX OF AMETHYST & CITRINE.
MILK QUARTZ OP. WHITE     AKA: SNOW QUARTZ, WHITE QUARTZ.
PRASIOLITE LEEK-GREEN     PRODUCED BY HEATING VL AMETHYST OR YWISH QUARTZ.  SUN FADES. 
ROSE QUARTZ STRONG-PALE PINK     COLOR CAN FADE.  RUTILE INCLUSIONS CAN PRODUCE  A 6 POINT STAR..
RUTILATED QUARTZ GOLDEN, REDDISH     QUARTZ CRYSTAL W/ RUTILE NEEDLE INCLUSIONS.
TOURMALINATED QUARTZ.  CLEAR W/GN OR BK     QUARTZ CRYSTAL W/ BLACK OR GREEN TOURMALINE NEEDLES.  .
AVENTURINE GREEN, RED/BROWN, GOLD/BROWN     IRIDESCENT SPARKLES.  TRADE NAME: “INDIAN JADE”.
PRASE LEAK-GREEN     OPAQUE AGREGATE.  AKA: EMERALD QUARTZ.
BLUE QUARTZ BLUE     TURBID AGREGATE. AKA: SAPPHIRE QUARTZ.
LEMON QUARTZ  YELLOW/GREEN      
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