People:
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):
John,
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
stone.”
There will be a quiz.
Rick Martin