Zeolites are a popular group of minerals for collectors and an important group of minerals for industrial and other purposes. They combine rarity, beauty, complexity and unique crystal habits. Typically forming in the cavities of volcanic rocks, zeolites are the result of very low grade metamorphism. Some form from just subtle amounts of heat and pressure and can just barely be called metamorphic while others are found in obviously metamorphic areas. Zeolite crystals have been grown on board the space shuttle and are undergoing extensive research into their formation and unique properties.
Zeolite Structure:
Zeolites compose a large family (46 varieties) of alumino-silicates.
Zeolite has a unique open, micro-porous molecular structure that, when seen through an electron microscope, has a honeycomb-like appearance with thousands of microscopic openings. These microscopic openings carry a natural, strong, negative charge.
How is Zeolite Formed?
Natural occurring zeolite is a crystalline mineral that has been formed from volcanic ash generally over a period of between 50 to more than 350 million years ago. During this time there were many violent volcanic eruptions ejecting millions of tons of ash into the air which fell on both land (to form topsoil) and into water where most was dissipated. But in the right conditions, in a few locations, natural zeolite deposits were formed.
To appreciate the uniqueness of zeolite deposits, it is necessary to understand the complex formation conditions that needed to occur, and the precise order in which they did occur, from the time the zeolite began as volcanic ash over 350 million years ago. These conditions and their order of occurrence are:
• After the eruption a thick layer of ash drifted far enough away from the eruption site so that all the heavy particles drop out and the ash contains no other materials in it except for the silicates;
• The ash must be composed of amorphous silica glass (called obsidian);
• The ash must have fallen, or be washed into water;
• The water must have been static and brackish (i.e. neither fresh nor salt water);
• The brackish water must have had the right type of various alkaline salts;
• The environment around the deposit must have been stable for a very long period (at least half a million years);
• This stability allows the amorphous glass to slowly re-crystalize and absorb the salts from the surrounding water;
• The ratio and concentrations of the various salts causes the formation of alumino-silicate crystals, a feature necessary to build the honeycomb structure;
• The deposit needs to have been placed under great pressure over at least a few million years to allow it to be compress into a hard rock mineral;
• The deposit needs to have been uplifted, preferably to where it was still covered and above where any subsequent flowing surface or sub-surface water would not contaminate it.
A good example to explain the way zeolite is formed is to compare it to the formation of ice. When snow falls it is light and fluffy, filled with air pockets. As the flakes accumulate they start to compact into a substance that takes on a crystalized form but is still easily crushed in one's hand. However, as the weight of snow increases, it compacts further into a solid substance, ice.
Volcanic ash is very similar. It can also fall very quickly and can cover everything on the ground very quickly. Remember the scenes of the 1991 explosion of the Mt. Pinatubo volcano in the Philippines, where the American military facilities had to be abandoned because of the tons of ash falling every hour. The same sort of eruption buried the towns of Pompeii and Herculaneum in Italy over 2,000 years ago in 79AD.
Types of Zeolite:
There are 46 naturally occurring zeolites that are known. There are more than 150 zeolite types that have been synthesized (produced artificially).
Although natural zeolites are a large family most of them fall into three distinct types:
• The first group contain zeolites that have chain-like structures made up of needle prismatic crystals. Asbestos and serpentine have similar type crystal structures.
• Structures resembling sheets where the crystals are flattened much like looking at a deck of cards, each card being a sheet. Clinoptilolite and mordenite are two examples of these.
• Structures where the crystals are more equal in dimensions, more like cubes. Chabazite is a well know zeolite of this type.
Zeolites of Coffee Pot Mountain Area:
Clinoptilolite occurs at several localities in the vicinity of Coffee Pot Mountain. These occur in a tuff bed 50 to 60 feet thick that is composed of a heterogeneous mixture of altered and unaltered vitrophyre (a volcanic rock with larger crystals embedded in a glassy groundmass) fragments and pyroclastics. Some of the tuff beds seem to have altered to zeolite minerals in a lake or from ground water. The vitrophyres possibly were altered by hydrothermal solutions, that could have originated in the volcanics, or by ground or surface water following the joints in the vitrophyre.
Zeolite Uses:
It is the zeolite's negatively charged honeycomb structure that makes the mineral so vitally important. It has given the mineral the ability to trap and remove many of the positively charged damaging toxins, chemicals and heavy metals that are all around us which have found their way into the food we eat, the water we drink and the air we breathe. Zeolites are used in ion exchange, filtering, odor removal, as a chemical sieve, and gas absorption. The most well-known use for zeolites is in water softeners.
Information from:
http://www.zeoactiv8.com/about%20zeolite.html (Natural Extracts Australia)
http://www.galleries.com/Zeolite_Group (The Zeolite Group of Minerals)
http://www.mines.az.gov/DigitalLibrary/ADMMR_Reprints/ZeolitesMR1.pdf (Consolidation of the Arizona Dept. of Mines & Mineral Resources with the Arizona Geological Survey)
In order to claim this earthcache, please email the answers to the following questions:
1. Describe the crystals as you see them (color, size, shape). Estimate the size of the largest crystal you can find.
2. Estimate the size of the largest zeolite cavity you can find. From your present location, how many zeolite cavities can you see?
3. What is the general color of the matrix rock in which the zeolite cavities are located?
4. According to the information given, what type of zeolites are found at this location? Why might the vitrophyre matrix have been altered from its glassy state?