Zeolite minerals (34 to 48 species, depending who’s counting) are natural sieves. Violent volcanic eruptions produce airborne tuff which is composed mainly of vitric ash. When this volcanic glass happens to fall into saline-alkaline water, such as that in a shallow lake, the glass is altered into minerals with a particular structure. Zeolites are hydrated alumino-silicate minerals that contain exchangeable alkali or alkaine-earth cations (positively charged ions).
Zeolite minerals can act as physical sieves, but their greatest value is their ability to exchange sodium, calcium, potassium, and magnesium in the mineral for other elements.
According to St. Cloud Mining, the major producer of zeolites in the U.S., zeolites “consist of an open, three-dimensional cage-like structure and a vast network of open channels extending throughout. Loosely bound, positively charged atoms called cations, are attached at the junctures of the negatively charged aluminosilicate lattice structure. The aluminosilicate framework provides exceptional strength and stability to the lattice structure.”
“The channels, typically 0.3 to 0.7 nanometers in diameter (3 to 7 angstroms, slightly larger than a water molecule), selectively screen molecules according to size and exchangeable cations. Molecules too large to pass through the entry channel are excluded, thus giving rise to the term ‘molecular sieve’.”
“The molecular structure, surface area, surface charge density, and cation exchange capacity of each particular zeolite will determine its loading, shrinking, swelling and stability under various conditions.”
“Zeolites have a rigid, three-dimensional crystalline structure (similar to honeycomb) consisting of a network of interconnected tunnels and cages. Zeolites in general have high specific surface areas and their rigid framework limits shrinking and swelling.”
Zeolites are used to help purify sewerage and other water, to purify sour natural gas, to treat animal wastes, to make plant food, and to remove cesium and strontium from liquid nuclear reactor waste. Zeolite is also used in the pressure shift devices called ‘oxygen concentrators.’ Someone on oxygen using a machine at home that makes ‘oxygen’ from the air, this is the stuff doing the work – the compressor sends air through this sieve material it scrubs the nitrogen out of the air and the trace gases with ‘oxygen’ pass though filters to the patient as ‘concentrated oxygen at about 94% purity. This process is used in some military jets to do the same thing – an F-22 has this type of oxygen system.
A large deposit of zeolite minerals occurs near Bowie, Arizona. This site produces the mineral chabazite and it is the only commercial producer of this mineral in the world. Bowie chabazite is pelletized and used for removal of carbon dioxide from low-BTU natural gases and the removal of radioactive elements from water. Bowie chabazite was used to mitigate the damage caused by the Three-mile Island nuclear accident. The Three Mile Island accident was a partial nuclear meltdown that occurred on March 28, 1979, in one of the two Three Mile Island nuclear reactors in Dauphin County, Pennsylvania. Zeolites are now being investigated to mitigate acid mine drainage problems.
Tucson geologist Ted Eyde (a friend of mine) was one of the original discoverers of the Bowie deposit. Ted’s son Dan is now president of St. Cloud Mining which operates the property as well as other zeolite properties in New Mexico, and Nevada.
Dan Eyde was interviewed recently on episode 35 of the Arizona Geological Survey’s weekly broadcast:
https://www.youtube.com/watch?v=G1N3B4TOlYA Dan Eyde starts at the 10:38 point in AZGS broadcast.
Now for the camels and cat:
When the volcanoclastic tuff was deposited at the Bowie site, it covered and preserved animal tracks in the underlying clay. As careful mining progressed, they uncovered tracks of camels and an extinct llama. As Dan Eyde described it during the interview, they found tracks which suggested that a small herd of camels was crossing the playa. They suddenly changed direction and started to run. Dan speculated that a predator came on the scene. Dan implied that they also found tracks of a saber-toothed cat at the site.
Rocks have many stories to tell. We just have to learn how to read them.
There are many other zeolite occurrences in Arizona (see first reference), but none are currently commercial.
Eyde, T.H. and Irvin, G.W., Arizona Zeolites, Mineral Report No. 1, State of Arizona Department of Mineral Resources (Link)
Eyde Ted H., 1982: Zeolite deposits in the Gila and San Simon valleys of Arizona and New Mexico. Circular – New Mexico Bureau of Mines and Mineral Resources 182): 65-71
Eyde, T.H., and Holmes, D.A., 2006, Zeolites, in Kogel, J.E., Trivedi, N.C., Barker, J.M., and Krukowski, S.T., eds., Industrial minerals and rocks (7th ed.): Littleton, CO, Society for Mining, Metallurgy, and Exploration Inc., p. 1039–1064.
Sheppard, R. A., T. H. Eyde and C. S. V. Barclay (1987). Geology, mineralogy, and mining of the Bowie zeolite deposit, Graham and Cochise Counties, Arizona. Zeo-Trip ’87: an excursion to selected zeolite and clay deposits in southwestern New Mexico and eastern Arizona. Brockport, New York, International Committee on Natural Zeolites.27-46 (Link)