Gold in the sky at cave Creek Campground, Arizona.
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The deal is that most of the black onyx on the
market is chalcedony (SiO2) that has been subjected to a dye. One of the simplest ways to achieve results
is to boil chalcedony in a solution containing dissolved sugar and allow the
stone to absorb the solution. Then
carbonize the sugar by applying sulfuric (mostly) or hydrochloric acid and voila - black chalcedony. However, the black color of the onyx is only
a few microns thick so any attempt at rough polishing or re-cutting would
reveal the non-black interior. It also
is my understanding that: 1) at times black glass is substituted for black
onyx; and 2) the sugar-acid solution is used on non-precious opal in order to
transfer the mineral to “precious” black opal!
Now, black onyx does exist in the natural world;
however, it is rather scarce. Onyx, by
definition, is a banded black and white form of chalcedony, similar to banded
agates. By far the most spectacular
black and white onyx that I have observed are the “eye agates” quarried from
Minas Gerais, Brazil, and cut into sphere or sphere-like forms resembling eyes. Sardonyx is a name usually reserved for
banded chalcedony with red to brown bands.
As I understand the situation, rockhounds prefer to use the name agate
for banded chalcedony with the bands being “wavy or non-parallel” while onyx
and sardonyx are reserved for agates with the parallel bands. Of course, some rockhounds freely use the
term agates for any piece of chalcedony, banded or not.
And, there is more confusion in the world of
onyx! Go to any rock show or tourist
shop in the western U.S. and you will see “onyx” carved into a jillion types of
bowls and animal fetishes or pipes or whatever.
Their color is usually a cream (or so) and all are banded with layers of
red to brown to yellow to all sorts of pastels.
However, these specimens are not composed of authentic onyx, that is
chalcedony (SiO2), but of some variety of limestone---a calcareous
(CaCO2) rock. At times this
“onyx” is really banded travertine formed around springs or caves or waterfalls
(see Blog posting on Thermopolis, Wyoming: 5-13-11). At other times the calcareous
“onyx” is a fresh water limestone. Most
of the calcareous “onyx” on the market was quarried (and perhaps carved) in
Pakistan or Mexico and usually is travertine.
But rarely are “raw” specimens labeled as to country of origin; however,
finished carvings usually have a small label attached stating “Product of
country.” I have also seen this “onyx”
sold as Mexican Marble or Onyx Marble.
During my past camping episodes in Arizona I tried
to run down quarries or mine dump piles and explore the offerings. Last year I visited an Arizona rock shop and
noted a huge hunk of what appeared to be travertine but was labeled Cave Creek
Onyx. So, I was off to investigate and
try to find the source of the hunk. I
could not locate much of scientific interest on the “onyx” but did find
references to the collecting locality on web sites or blogs where the authors
had collected specimens. The Arizona
Geological Survey had produced a photo of the quarry for one web site and an
obscure publication, Stone: An Illustrated Magazine, Vol. 5, No. 5, October
1892, pp. 289, noted: “So far as developed, the Cave Creek
onyx beds do not seem to be as large as the Yavapai beds [probably Mayer, see
below], though the stone is as fine, but even as they are, they will produce
large amounts and in blocks of very satisfactory size. J. B. Dougherty, of New
York, is doing a great deal of development work, and as soon as the road is
completed, he will put teams to hauling and loading it on to the cars at
Phenix, for shipment to New York. – Phenix Gazette.” So,
off I go in search of the “onyx.”
I did locate the old
quarry by heading north from Carefree, Arizona, on the Camp Creek-Seven
Springs-Bloody Basin road. The road goes
through typical desert scrub; however, there are a couple if interesting sites
along the trail. One is the Sears-Kay
Ruins, a 40 room village built around 900 years ago and constructed by people
of the Hohokam Culture. It is built on a
hill and has spectacular views of the surrounding foothills, and has a nice
hiking trail winding through.
Continuing up the road,
rockhounds drive through the Seven Springs area where sycamore trees line
permanent water flowing from local springs.
There is a recreation area located along the creek that is the site of a
former Civilian Conservation Camp (CCC).
The area really is a jewel in the desert.
The old “onyx” quarry is
located upstream from Seven Springs and seems out of place in this desert
environment of volcanic rocks of all sorts.
The deposit has been known for years but I am uncertain about the total
tonnage removed, or when the quarry was closed for commercial use. Townsend
(1961) implied that the quarry was closed by 1961: “Near Cave Creek in Maricopa
County, greenish and yellowish onyx with veins of brown and red is deposited in
intimate association with basalt. Although of fine quality, only relatively
small pieces may be removed due to shattering by volcanics.”
A boulder in wash too large for a haul home, FOV
~four feet! Note travertine on right
attached to a volcanic agglomerate on left.
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As best that I can tell
the “onyx” is a freshwater limestone (Gilbert and other, 1998), or perhaps a
travertine (Anthony and others, 1995). I
believe the quarry in situated in what Gilbert and others (1998) mapped as “Tcl of Late Oligocene and Miocene Age:
Conglomerate and limestone--Conglomerate and sandstone, mostly of granitic
origin, interbedded with thin- to medium-bedded white, lacustrine limestone.
The limestone is typically recrystallized, but locally preserves ooid-pisoid
grainstone/packstone textures and stromatolites. The unit is interbedded with
subaqueous basalt lava flows.”
Algal mats with recrystallized calcite,
stromatolites. Width FOV ~ 5 cm.
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Cut slab of Cave Creek Travertine. Width ~12 cm.
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Reverse of above figure. Note beds of algal mats perpendicular to
upper surface.
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For the rockhound, the quarry seems accessible and perhaps on public land (Do not take my word for this, check with the USFS, Tonto). I picked up as many specimens that I wanted of baseball-softball size in a small drainage fronting the abandoned quarry. I actually did not attempt to go near the quarry wall since the space between the creek and the wall is filled with brush, many with spines, and I observed two beautiful rattlesnakes with 10 feet of hiking to the face. It was a nice sunny day and these two gentlemen were out sunning.
Perhaps the most “famous”
onyx marble collecting locality in Arizona is near Mayer, Yavapai County, where,
according to numerous non-technical sources, considerable amounts of white to pale green to cream to brown to
yellow banded “onyx has been produced. Anthony and others (1995) noted that the Mayer
“onyx” is actually calcareous travertine.
Evidently the deposit has been known, and mined, for several decades as
the Archives in the Arizona State Library note that “more than 1 million pounds
of onyx were shipped in 1922. The onyx
was made into lamp stands, jewelry boxes, church alter rails, tabletops and
other ornamental items. In 1927, seven
automakers, including ford, were using Mayer onyx for decorative detailing in
their cars.” This latter statement was
sort of fascinating to me.
Unfortunately, I have been unable to locate photos or descriptions of
these onyx accessories.
As best that I can
determine, the Mayer quarry did not operate commercially from sometime in the
1930s until reopening in 2001 by a company called Stoneworld International. The
company noted that a core drilling study revealed that the deposit of onyx is
at least 55 meters deep (Stoneworld, 2005).
That seems to me a phenomenal thickness of travertine. The modern quarry produces, and markets, two
colors of onyx: Grand Canyon Onyx, with brown, red, white and green, and
Black Canyon Onyx, with black, gray, dark brown and white. (Above from Stoneworld, 2005). But again, the onyx is really travertine.
I was unsuccessful in
locating geological information about the Mayer deposit other than thinking the
travertine is Quaternary in age. Of
course, I am not an Arizona native rockhound and could not find a local person
with additional geological knowledge about Mayer. But, I liked the specimen for sale at a rock
show and snapped it up for three bucks.
Banded calcite with massive brown crystalline calcite
in lower third. Width of specimen ~7 cm. Grapevine Canyon.
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I know even less about a
banded calcareous stone picked up at the same show that was collected at “Grapevine
Canyon southeast of Flagstaff.” It also
was labeled “onyx” but does not appear, at least to me, to be travertine but some
sort of a banded piece of calcite. The
seller was quite hesitant about divulging a more precise location! I have hunted in detail for references about
rocks at Grapevine Canyon, especially travertine or onyx, but have been mostly
unsuccessful. The only real clue is a
website called “agates with inclusions” that has four photos, but no other
information, of “Grapevine Canyon Plume Onyx” that pretty much matches my
specimen. The canyon is located in the Chavez
Mountain NE topographic quadrangle near Morman Lake. MinDat, in its list of minerals for Coconino
County, noted “calcite: var. limestone onyx.”
Again, I am certain that a more experienced Arizona rockhound would be
able to supply additional information on this locality.
So, I have learned much from
this little exercise, especially that one cannot believe everything one reads—Mayer
onyx advertised all over Arizona is not “real” onyx---and that locating
geological information about some localities is sometimes difficult for a non-native
rockhound! But, learning is a very
necessary part of the process of life.
It
is not knowledge, but the act of learning, not possession, but the act of
getting there, which grants the greatest enjoyment.
Carl Friedrich Gauss
REFERENCES CITED
Anthony, J.W., S.A.
Williams, R.A. Bideaux, and R.W. Grant, 1995, Mineralogy of Arizona, Third
Edition: Tucson, University of Arizona Press.
Gilbert, W.G., A.C. Ferguson, and R.S. Leighty,
1998, Geological Map of the Homboldt Mountain 7.5’ Quadrangle, Maricopa County,
Arizona: Arizona Geological Survey,
OFR-98-11, scale 1:24000.
Stoneworld, 2005: www. Stoneworld.com
Townsend, R.C., 1961, Stone in Arizona, private report
for Arizona Development Board.
Hello, thanks for this great article. I'm a rockhound and recently visited the Seven Springs area for jasper, which is pretty nice quality. Just by chance, I was driving on some of the residential roads above Carefree and spotted the tip of a jasper-looking rock at the side of the road, in a gully. I was able to dig it up (~80lbs) and after cleaning it off I'm wondering what I've got. It looks like it has bands of red jasper, maybe some cream-colored onyx, and a couple knobs of more clear agate (or quartz-looking) material included for good measure. I don't want to cut or break it up - rather, I'd like to clean it up and see if I can make it an attractive piece for display. When the stone is wet and in the sun, it shows off a lot of color - reds, orange, yellow, cream. But when it's dry and inside, it's a rather ordinary tan rock. ;-) You may not know the answer to this question but I'm curious if it's advisable to treat the rock with some kind of sealant which will bring out the color, and give it a little shine. I was thinking about getting some stone floor sealant from the home improvement store and trying that. The rock has so many indentations and rough areas that I don't think it will be feasible to try and grind/sand it down to achieve a smooth surface, but i do have the tools for that. Any advice you could provide would be much appreciated. I'd like to bring out the best colors in indoor lighting conditions, but I've never tried sealants before.
ReplyDeleteI have the same question. I'm a Midwesterner but have picked up some nice specimens off of Spur Cross Rd. and far East off of Cave Creek Rd. We were there last week and I picked up a beautiful yellow-green stone about six inches long and very smooth. Any ideas on what it is? Thanks so much.
ReplyDeleteI am currently creating hand carved art pieces out of the "onyx" from the Mayer mine in Arizona my customers want to know the metaphysical properties of the stone but I can't be sure what it actually is it dose not look like any travertine I have ever seen it's labeled as Black and Grand Canyon Onyx it looks like a Banded Calcite but is to hard to be calcite
ReplyDeleteThe black canyon is brown red black and white
The grand Canyon is white black yellow green and brown
I was hoping you would share your thoughts on what it is
the black canyon onyx and grand canyon onyx, are mostly banded calcite. tests with acid will easily confirm if an "onyx" is chalcedony or carbonates like calcite. travertine is a sedimentary rock, almost pure calcium carbonate, but a different structure than calcite. i have put many pieces of arizona "onyx" into a light acid bath, called "acid washing" and they were polished by the acid. i do not believe you can polish travertine with acid, as it is said to destroy the finish even in weak amounts. but acid will destroy calcite as well, if not done properly. my personal opinion is that arizona "onyx" and mexican cave onyx etc are mostly types of banded calcite. i even have a piece of "onyx" from pakistan, and i was able to polish it with the same methods i use for calcite. which to me, says that it is mislabeled calcite. many items being sold as banded travertine, look like banded calcite as well. as calcite is the "commonest carbonate" according to a book i am referencing, it would make the most sense for these items to be calcite, not travertine.
ReplyDeletewhoever started calling a carbonate, onyx...really, truly messed things up. we need a new definition/clarification for "onyx."
from "simon and schusters guide to rocks and minerals"
ReplyDeletetravertine components:
calcite or aragonite, with limonite impurities; frequent fossils and imprints, especially of plants.
type: chemical sedimentary rock
class: carbonatic rock
CALCITE:
group: carbonates
composition: CaCO3
Appearance: Rhombohedral, scalenohedral or prismatic crystals, often intergrown or twinned. Variable color (colorless, white, pink, green, yellow, etc.). Occurs in masses: compact, microcrystalline (limestones), saccharoidal (marbles), fibrous (alabasters), concretionary (stalactites and stalagmites), pulverulent, oolitic, etc.
-technically, calling banded travertine, banded calcite, would be correct, if the travertine is made up of calcite.
-technically calling banded marble, banded calcite, would be correct, as marble is a coarse grain variety of calcite
-technically calling banded alabaster, banded calcite, would be correct, as it is the fibrous variety of calcite
basically, they are all calcite...and if they are banded, they can be considered banded calcite.
Awesomme blog you have here
ReplyDelete