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[abused term] Onyx

 True onyx is calcite (calcium carbonate) 

Since this basic appeared in two succesive letters,
I have to respond: No, no, no!! “Onyx” is a much-abused term.
(No offense intended…the terminology below has been established
for many years).

True onyx is natural black and white parallel-banded chalcedony
(a quartz mineral). It was prized in antiquity for cameo
carving, with one color or the other as the base with the other
in sharp raised relief. It was also used for intaglios, another
form of gem carving in which a design is incised into the stone
instead (negative relief, often used for seals).

Sardonyx is also a natural chalcedony with layers of sard
(similar to carnelian in color but more brownish and opaque)
alternating with layers of black and white. It sometimes occurs
as sard with white only.

Most of the “black onyx” so popular today is dyed chalcedony.
There are other dyed “onyx” colors: green, red, blue, etc. Most
of these stones are produced in Germany. Some black chalcedony
occurs naturally.

None of the above should have shown the pitting described in the
letter about the beads. Banded calcium carbonate (calcite onyx)
is often referred to incorrectly as “onyx” or “Mexican onyx”,
probably because it exhibits parallel banding reminiscent of true
onyx. The explanation of calcium carbonate reacting with acidic
perspiration makes sense. Most of it is “polished” by immersing
carved pieces in a mixture of sulphuric, nitric and hydrochloric
acids. The acid-carbonate reaction provides a quick surface
gloss with no sharp corners (as in the numerous ashtrays and
chess sets produced cheaply in Mexico from material mined at El
Marmol in Baja California).

There are many very beautiful types of calcium carbonate that
are collected and cut. They range from “cave onyx” (aragonite)
to a wide range of colorful and patterned varieties that bear
descriptive or place names. But they are not true onyx.

Rick Martin


Mr. Martin, I’m still not greatly closer to whether these beads
are a quartz stone or something else–what do you make of the
hardness of 6-7?

Colene Abramson


Chalcedony (onyx) and quartz fit neatly into that hardness
range, usually 6.5 to 7.5. I’ve been working with these stones
most of my adult life (a long time!) and I’ve never encounted
such a thing. I simply don’t have an explanation without seeing
them, and maybe not even then. Could they be hematite (hardness
5.5-6.5)? If so they would be metallic black, and heavier than
most beads. Moisture such as perspiration over a period of time
could conceivably cause pitting. Marcasite and cassiterite
(iron and tin, respectively) are marginal possibilities.
Otherwise, I simply don’t know. Rick Martin


Chalcedony, that’s what" onyx" is. Wether it’s the genuine
article, or the “black onyx” type( dyed black chalcedony).


Sometimes black jade (nephrite) will show pitting, especially on
the end-grain. Will E.


G’day; from The Dictionary of Geological Terms (American
Geological Institute):

ONYX; (1) A cryptocrystalline variety of quartz made up of
different coloured layers; chiefly white, yellow, black or red (2)
Translucent layers of calcite from cave deposits, often called
Mexican onyx, or onyx marble.

Thus, it can be an agate, calcite, or a form of marble. Though
I disagree with the latter definition; marble is a metamorphosed
rock (altered by natural heat) whilst calcite and cave deposits
come from sedimentary calcium carbonate which is recrystallized
from aqueous solution. So, as far as I can make out Onyx is like
beauty - in the eye of the beholder; Yer pays yer penny an’
takes yer choice. Cheers, John Burgess


My gemology is rusty,but this does not sound right.Calcite is
not a quartz.True Onyx is a calcite,and very soft,hardness
3-4.Sounds like the Dictionary is confusing the trade name
"Onyx",like in Black Onyx a dyed gray Agate.Very hard,7-8.Agate
is cryptocrystalline Quartz.They have taken a centuries old
misnomer and made it official.They are both fruits,but an apple
is not an orange. Mark Liccini


Hi Mark, True onyx is not calcite, but is a black and white
banded agate. Years ago, pen holders were made from travertine
calcite and marketed as “Mexican Onyx”. It’s name was derived
from the banded appearance of the stone. Over the years all
banded travertine was called onyx by dealers, but not by
gemologists and mineralogists. To complicate matters, the black
and white material became scarce and stones cut from just the
black agate was being called onyx. Black dyed agate is also
called onyx. But the true onyx remains the banded black and white
variety of agate. Will Estavillo,


I don’t think it’s quite so cut and dried. Frederick H Pough’s
book, A Field Guide to Rocks and Minerals, lists onyx as a form
of calcite, so it is not only dealers who consider onyx to be a
form of banded calcite. Lee Einer

True onyx is not calcite, but is a black and white banded

Hi Will,My post was edited,including the title.I was questioning
this definition: from The Dictionary of Geological Terms (American
Geological Institute):

ONYX; (1) A cryptocrystalline variety of quartz made up of
different coloured layers; chiefly white, yellow, black or red
(2) Translucent layers of calcite from cave deposits, often
called Mexican onyx, or onyx marble.

I don’t think an onyx is a black and white agate.I think a black
and white agate is a black and white agate. I think I like to use
the definition for Onyx I see up at “Yavapai onyx” This unusual
variety of travertine formed by hot spring action along an
ancient fault in northern Arizona is a wonderful medium for
carving, if you can find pieces that are free of fractures and
display great patterns, that is.

I guess you are really selling Yavapai black and white agate?
Mark Liccini


Funny, all my mineralogy text books and indeed, all my geology
texts and all my professors as I was getting my degrees, said
onyx as a form of banded chalcedony and that’s what we taught
our students as well. But then I’m a geologist by training, not a

Lynn A. Davis
Tephra’s Treasures
Handcrafted Jewelry, Accessories
And Other Fine Treasures


The proper term for what you are describing as calcite onyx, is
marble onyx which has no connection with the dyed black
chalcedony sold under the name of “black onyx”.


Why don’t we settle the Onyx question once and for all and admit
that popular usage will settle the matter down the road. All
this technical hair splitting overlooks the fact that onyx and
sardonyx are, for all intents and purposes, ABUSED
chalcedony…agate which has been soaked in sugar and then
immersed in acid becomes black onyx and sardonyx is usually the
result of heating ordinary banded agate. Let’s just call the
travertine type of onyx, calcite onyx…oh gawd! Here we go
again…popular usage has it that travertine is that butt ugly
,beige, hole ridden stuff that makes early neuter style coffee
tables. This issue is becoming so polarized that the agate
people will have to join up with the calcite schism to fend off
the Travertine faction. Maybe Osama Bin Laden will recognize
this as an opportunity to divide and conquer!!! Ron at
Mills Gem, Los Osos, CA.

    I guess you are really selling Yavapai black and white
agate? Mark Liccini <grinning> 

Hi Mark, The use of the names Mexican onyx, Yavapai onyx, onyx
marble, and a few others is not the issue. These terms describe a
banded variety of calcite/aragonite, which may or may not
resemble “True Onyx”, which is a banded black and white
cryptocrystalline quartz mineral. The use of the name onyx
without a qualifier, implies true onyx. Lets take another gem
material as an example of the problem, Jade. True jade is either
nephrite or jadeite. African jade is green garnet, Indian jade is
aventurine quartz, Korea jade is almandine garnet, Manchurian
jade is soapstone,Transvaal jade is grossularite garnet, new jade
is serpentine. The issue then, is the use of a name to describe a
specific mineral or gem vs. the use of a name to describe a
quality, color, appearance, or similarity to a specific gem by
another mineral. Yavapai onyx is not a true onyx even though 30%
of it comes as black and white banded material. I would never
call it onyx, or true onyx, but I suppose I could call it " An
iron, manganese rich black-red-yellow-white banded stalagmitic
calci-aragonite". But then again, the ancients mined this stuff
near Thebes and called it onychites, onyx. Will Estavillo


Hello Lynn,

I am neither a jeweller nor a geologist but I have a modest
library and I am amused but sympathise with those who wince at
the deceptive misnomers and misleading names that some jewellers
are want to bandy around willy nilly. I am enjoying the
compilation of a list of my favourites and hope to put it
on-line soon.

My references also show Onyx to be the black and white banded
variety of Chalcedony and so the correct term would be Onyx
Chalcedony or Chalcedony Onyx. Travertine Onyx and Onyx Marble
are also correct terms which explicitly identify a particular

The problem with using the word Onyx however is that this is
only part of a name and is meaningless without the rest of it.
Calling it Black doesn’t help that’s a colour not a variety of
anything. By any scholastic measure Onyx, Black Onyx and
Jewellers Onyx may be whatever the jeweller wants to use to
obtain the desired effect, lignite, chert, glass, spinel,
dravite, sapphire, etc., are all valid candidates. There is no
REAL Onyx, grinding away the white and calling Onyx Chalcedony
the real Black Onyx is as deceptive and misleading as using any
of the above candidates.

Public acceptance, recognition and sales however have more
meaning and relevance to the average jeweller than any pleas for
correct mineralogical nomenclature, especially as Onyx has almost
no real value no matter what material is being offered. I make
no charge to my customers for supplying the blonyx for custom
cabochon or inlay jobs, just my labour charges for the work

TTWISI…Tony. Art Jewellers On-Line Gallery and promotional
collective for jewellery artisans. To subscribe to our newsletter
please visit;



I don’t know what it takes to put arguments over terminology to
rest. I wrote the following a few days ago in response to John’s
post from the geological dictionary cited below, then decided I
was probably picking fly specks out of the pepper and didn’t send
it. But the discussion seems to go on and on, and now I think
it’s relevant.

Let me say there is an ongoing dispute between mineralogists and
gemologists over terminology. No mineralogist is ever going to
call green grossular garnet “Tsavorite” or blue zoisite
"Tanzanite." And even if Frederic Pough (a prominent
mineralogist and someone I admire enormously) calls calcite
marble onyx “onyx,” that isn’t necessarily the gemological
definition. Each discipline has its own jargon for its own
reasons so there will probably never be total agreement between
the two. It’s confusing, but that’s life. I also realize that
what’s “correct” in the dictionary isn’t necessarily the
terminology of the marketplace.

What follows is materially the same I posted on this
topic a couple of weeks ago.

   Onyx: The Dictionary of Geological Terms (American
Geological Institute): 


Since we’re going to the dictionaries, and since we’re
discussing a gem material instead of a geosyncline or a
discontinuity, here’s what the "Dictionary of Gems and Gemology"
by Robert M. Shipley, issued by the Gemological Institute of
America has to say:

“‘Onyx’ : Commonly used, but nevertheless incorrect name for (1)
solid-colored chalcedony. (See ‘black onyx’; ‘green onyx.’ (2)
Marble and similar materials used in ornamental and utilitarian
objects, an even more confusing usage. See ‘black onyx’”; ‘green
onyx’; onyx; onyx marble.

“Onyx: One of the many varieties of chalcedony. Same as banded
agate except that the alternately colored bands of onyx are
always straight and parallel. Stones most common are black and
white or gray, black and red to brownish red, but those banded
only with grays or gray and white are more specifically known as
onyx agate. Stone cameos are carved principally from onyx. The
term onyx used except as a qualifying adjective for other than
parallel-banded multi-colored chalcedony is incorrect. See
’onyx”’ carnelian onyx; sardonyx. (2) Qualifying adjective
meaning parallel banded as in the term ‘onyx marble.’

"Onyx Marble: A translucent compact variety of calcite
generally deposited as stalagmites; with parallel bands usually
irregular, curved or bent. Colors usually white, often grayish,
brownish or reddish. Dyes easily and is marketed in several
natural and dyed colors in many parts of the world under
incorrect names, including ‘onyx,’ ‘Brazilian onyx,’ ‘Mexican
onyx,’ ‘Mexican jade,’ Gibralter stone, ‘Egyptian alabaster,’ and
’oriental alabaster.’ The alabaster of the ancient world.

‘Black Onyx’: Incorrect name for black single colored agate or
chalcedony which is usually colored artificially. Properly called
’black chalcedony.’ "

To give the British school of thought as equal a hearing as
possible from my limited library, the following is from Dr.
B.W.Anderson’s “Gem Testing.” (The late Dr. Anderson was director
of the Precious Stone Laboratory of the London Chamber of
Commerce, Diamond, Pearl and Precious Stone Section; and Lecturer
in Gemmology at Chelsea Polytechnic, London.)

Under the heading “Agate,” he says: “When required for ornament
it is stained by a variety of chemical means to enhance the
contrast of the various layers. Where the bands are straight the
names ‘onyx’ (black and white), ‘sard’ (red), ‘sardonyx’ (red and
white) are used. Cameos are often cut from such material, the
carved relief being worked in the white layer with the underlying
black or red layer acting as an effective background. Black onyx
is produced by saturation of the natural grayish material with a
solution of sugar or honey, and subsequent treatment with
sulphuric acid, which deposits carbon in the pores of the

There will be a quiz.
Rick Martin