At this location, zeolite crystals are prominently displayed on an igneous boulder. Zeolite is a hydrated alumino silicate mineral. This feature is uncommon, and not often seen in such a visible and accessible area like Launceston's Cataract Gorge Reserve.

Logging Requirements

To log this EarthCache, answer the following questions and message your answers to the CO:

1. Of the three distinct family structure types of zeolite (chain-like, sheets, or cubes), what is this zeolite? [refer to Types of Zeolite section]

2. (a) Describe the colour and crystal habit of the zeolite that is evident here.
(b) Based on the table and associated photos [as per Types of Zeolite section], and the zeolite family structure (Question 1 answer), what zeolite specimen do you think is present here?
(c) Why, providing comment to answers provided as per 2(a) and 2(b)?

3. (a) Estimate the coverage of zeolite on the boulder (e.g. 10%, 50%, 80%, etc.).
(b) Based on this coverage, do you think this location was a good example for this area to satisfy all of the necessary zeolite formation requirements?

4. Take a photograph with yourself (your face) and/or your geocaching name (written on a piece of paper or your hand) in front of the boulder that displays zeolite. This photograph must be attached to your find log.

Introduction

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.

Chemical 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.

(Ramsay and Kallus 2000)

Formation

Zeolites are formed by changes that occur in volcanic rocks when in contact with fresh- or seawater. 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, many violent volcanic eruptions were ejecting millions of tons of ash into the air which fell on both land (to form topsoil) and into the 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 dropped out and the ash contained 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 been 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 compressed into a hard rock mineral; and
• The deposit must have been uplifted, preferably to where it is still covered and above where any subsequent flowing surface or sub-surface water would not contaminate it.

Types of Zeolite

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; and
• Structures where the crystals are more equal in dimensions, more like cubes. Chabazite is a well-known zeolite of this type.

There are 46 naturally occurring zeolites that are known, and more than 150 zeolite types that have been synthesised (produced artificially). A few examples of the zeolite family include the following:

Use

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, odour removal, a chemical sieve, and gas absorption.

The most common use of zeolites is industrial for removal of heavy metals during purification in water management. Zeolites are routinely used in water management systems and for animal feed purification. Animal studies have been conducted to evaluate the ability of zeolites to remove heavy metals from biological systems and have been shown to be effective.

(Purushothaman 2018)

Due to the rare quality of this zeolite specimen, do not touch the crystal formation.

References

• Drisko, Jeanne A. (2018) - Integrative Medicine, Edition 4, https://www.sciencedirect.com/science/article/pii/B9780323358682001079.
• Ramsay, J.D.F., and Kallus, S. (2000) - Zeolite Membranes, Membrane Science and Technology Volume 6, pp.373-395, https://www.sciencedirect.com/science/article/abs/pii/S0927519300800169.
• Purushothaman (2018) - Zeolite process for water softening (Permutit process) - Water technology, https://youtu.be/a273pRy8bHk.
• ScienceDirect (2022) - Zeolite, https://www.sciencedirect.com/topics/medicine-and-dentistry/zeolite.
• Sorrell, S. (2003) - The Distribution and Occurrence of Zeolites in Tasmania, Page 16, https://crocoite.com/wp-content/uploads/2019/09/zeolites.pdf.
• Wikipedia (2022) - Zeolite, https://en.wikipedia.org/wiki/Zeolite.