Gold in the sky at cave Creek Campground, Arizona.
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.
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.
Cut slab of Cave Creek Travertine. Width ~12 cm.
Reverse of above figure. Note beds of algal mats perpendicular to upper surface.
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.
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
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.