AGATES - ORBICULAR JASPER - PETRIFIED WOOD
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AGATES
Agates are a favorite semi-precious stone that most seasoned beach combers hunt for while exploring a beach. They are found throughout the Pacific Northwest and most of the U.S. in different shapes, color, banding and opacity. Of all the beautiful stones found on a beach, agates are typically the most beautiful and prized. In order to aid the agate hunter in a successful search detailed information will be given about agate formation, types and quality. Additional information will guide the agate hunter in how to find agates on a beach, where to look and agate identification. WHAT IS AN AGATE? How about a little technical information. Info provided by http://www.agatelady.com/agate-basics.html Agates are semi-precious gemstones that are a variegated form of chalcedony (pronounced kal-sed'-nee), which is silicon dioxide in the form of microscopic fibrous quartz crystals. Agates naturally develop when an empty pocket inside a host rock fills in molecule-by-molecule, layer-by-layer as these microcrystals self organize to form concentric bands or other patterns. The colors and arrangement of the microcrystals are influenced by changes in pressure, temperature, and mineral content that occur during the formation process. Unlike other gemstones, each agate is unique. Even slabs cut from the same specimen will vary in color and design. HOW DO AGATES FORM? Agates develop as secondary deposits in hollow cavities, called vesicles. Although they can form in all types of host rock, most of the world's agates developed in ancient volcanic lava. When the continents were first forming, layers of molten lava pushed toward the earth's surface through rift zone cracks, volcanoes, and other geologic events. Within the lava, there were pockets of trapped gases. Later, these gases escaped through cracks that formed as the igneous rock cooled and hardened, leaving hollow cavities. Other cracks and seams also formed when adjoining sections of lava cooled at different rates. Agate Microcrystal Formation These empty cavities and seams filled with fluids rich in dissolved and suspended quartz molecules (silica), as well as other mineral impurities. When the silica concentration became supersaturated, it developed a gelatin-like consistency either throughout the pocket or in a layer that served as the active crystallization front. Over time, the silica molecules began to form miniature fibrous microcrystals that attached to the sides of the cavity or seam. During the filling-in process other mineral impurities collected at the inside of the chalcedony silica band, forming intervening and often contrasting bands. This pattern repeated until the entire vesicle was filled in, or until all the silica rich solution was used up. If there was the proper balance of silica and mineral impurities, then the entire cavity filled with alternating bands. If there was an insufficient quantity of mineral impurity or if the pressures and temperatures changed, the cavity completed filling in with macrocrystalline quartz, or another form of silica. |
Carnelian agate with banding found on Damon Pt., Ocean Shores, WA
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Types of Agate
There are thousands of different types of names given to agates found throughout the world. Sometimes agates are named because of their formation type, such as a fortification agate. In other cases, they are named after the location in which they are found, such as the Lake Superior Agate. Sometimes, it is a combination such as a Lake Superior Fortification Agate. Below are a few examples.
There are thousands of different types of names given to agates found throughout the world. Sometimes agates are named because of their formation type, such as a fortification agate. In other cases, they are named after the location in which they are found, such as the Lake Superior Agate. Sometimes, it is a combination such as a Lake Superior Fortification Agate. Below are a few examples.
Fortification Agate - This is the most common and distinctive type of agate. In these agates, bands crystallized into concentric layers that more or less follow the shape of the cavity. The banding resembles an aerial view of a fort.
Water-Line Agate (aka-water-level or onyx) - During its formation, silica-rich solution either entered the cavity slowly laying one band at a time, excess water drained out leaving a small amount of silica to settle out into separate bands, or the vesicle filled under low pressure. In this type of agate, the silica crystallization in water-level agates is controlled by gravity creating one orientation, forming multiple levels of parallel bands.
Tube Agate - During the formation of some agates, parallel projections of tiny hair-thin mineral rods grow first within the silica gel, around which later the chalcedony agate micro-crystals form. In some cases the inclusions remain, but sometimes they weather away leaving hollow tubes that subsequently fill in with silica.
Eye AgatesThis peculiar agate characteristic is believed to be formed when most of the silica gel drains from the cavity, leaving only a droplet that “beads up” on the inside wall of the cavity. This droplet crystallizes into solid chalcedony “eyes”. In some cases, crystal growth will continue from this droplet in a manner similar to the formation of stalactites in caves. Later, the pocket fills in with the usual deposition of chalcedony microcrystals.
Plume AgateThese agates initially had formations on their outside layer that formed prior to the deposition of chalcedony bands. They are filament growths of mineral inclusions that resemble ferns or feathers.
Geode Agate - In some cases the supply of silica-rich water runs out before the entire cavity fills in. When there is a hollow center within a crystalline outer fill, the specimen is considered a geode. Not all geodes have agate banding, but many do. Also, the inner layers can form into several different types of silica mineral crystals and may even have other types of mineral crystals.
Moss Agate - These agates have clusters of mineral inclusions that resemble plants, trees, or landscapes. Most moss agate inclusions are comprised of iron or manganese oxide. In some cases, the inclusions inhibit chalcedony banding allowing the mineral clusters free reign to grow within the silica gel.
Seam Agate - These agates form in cracks within host rock, rather than in rounder pockets or cavities. The bands form in parallel rows that follow and fill in the crack or seam.
Where to Find Agates - Agates are actually embedded everywhere on a beach. If a beach is located within range of a natural water way where agates are regularly flushed out of the hills, then you will find agates. The next difficulty will be assessing the right locations on a beach to hunt.
Gravel Beds - The best place to locate agates on most beaches is in areas where gravel beds occur that have accumulated large quantities of rocks of various sizes. The natural process that concentrates gravel in some areas and sand in others will guide the agate hunter toward the most productive areas to explore. You will notice that a beach will have areas with fine gravel, medium size gravel and larger stones. This will help you to explore certain areas that will produce the kind of agates you are looking for. I have at times found a larger agate sitting on top of a finely grained gravel bed as if it has just been washed up. This will occur from time to time, but on the whole most agates are consistently embedded in rock beds with similar sized stones.
Tide scheduling - In order to plan your hunt and find the most agates, you should consult a good tide schedule that will detail when the tides will be at their lowest. Knowing when the tides are lowest will help the agate hunter anticipate when the agate beds will be exposed to their greatest extent to allow adequate time to carefully hunt.
Careful Examination - I have been on the beach many times and was passed by beach walkers who said they were looking for agates. I noticed, though, that they were simply in too much of a hurry and not allowing for a careful examination of the rocks below and around their feet. I have located amazing nuggets that were just recently by passed with foot prints all around them and wondered how it could have been missed. I have also noticed that if I just rotated my position and examined the same gravel area from another angle I could locate agates. The angle of light or just a different perspective caused my eyes to fall on embedded nuggets that were either on top of the rock bed or lying among the rocks. The mind is a powerful filtering tool if you concentrate on finding only certain objects. I have found that if I concentrate on certain objects that glow, have a certain color or surface texture then the agates will jump out from the gravel beds. This requires focus and you really can't walk at a regular pace on the beach. The agates are typically distributed over the gravel beds so I haven't found it to be advantageous to sit down and dig. The only time this proved to be helpful was on Murdock Beach looking for agatized fossils that were embedded in the gravel beds.
Identifying Agates
The predominate types of agate found on the Pacific Northwest beach fall within the categories of seam agate, geode agate or fortification agate. The agates found on the beach have been greatly reduced by the tumbling action as a result of their journey from their original location and formation in host rock. Their journey downstream and out to sea to be deposited onto a beach where continuous surf tumbling occurs produces a significantly diminished stone. Agates, however, are some of the hardest rocks on the beach and will resist the rounding and reducing effect of surf tumbling when compared to the many other basalt, granite, jasper and quartz rock types found. These other types are found on the beach with a far greater rounded and smoothed appearance. Agates typically are found with many of their original inclusions and shapes that are left illustrating the impressions of the old host rock that formed them.
The most important identifying characteristics of agates on a beach are: opacity, color, banding and pitting.
The predominate types of agate found on the Pacific Northwest beach fall within the categories of seam agate, geode agate or fortification agate. The agates found on the beach have been greatly reduced by the tumbling action as a result of their journey from their original location and formation in host rock. Their journey downstream and out to sea to be deposited onto a beach where continuous surf tumbling occurs produces a significantly diminished stone. Agates, however, are some of the hardest rocks on the beach and will resist the rounding and reducing effect of surf tumbling when compared to the many other basalt, granite, jasper and quartz rock types found. These other types are found on the beach with a far greater rounded and smoothed appearance. Agates typically are found with many of their original inclusions and shapes that are left illustrating the impressions of the old host rock that formed them.
The most important identifying characteristics of agates on a beach are: opacity, color, banding and pitting.
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Opacity (translucent quality) - All agates are very translucent when held up to the light. Even the beginner beach comber will notice the translucent quality of an agate as they explore a beach. The agate is far more brighter than most other rocks on the beach. When approaching an agate lying in a rock bed surrounded by thousands of other rocks, the agate will actually shine because of the amount of light that is able to pass through it. Approaching a bed of rocks with the sun in front of you will allow the translucent rocks to shine in all their glory! They will stand out like beacons.
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Here's a little technical information about what the words "transparent, translucent and opaque" actually mean when rocks are concerned. Reference: https://www.gemsociety.org/article/gemstone-transparency/
Opacity, Translucence, and Transparency
The more wavelengths of light a gemstone absorbs or reflects, the more opaque it is. (Both a solid black object and a mirror, for example, are considered to be opaque). The more light that is absorbed or reflected means there is less light to transmit through the gem.
A translucent gem can transmit enough wavelengths of light that we can see light shining through it. However, if the wavelengths of light that escape the gem are highly scattered, due to the gem’s refractive index (RI) or other physical properties, light is all we can see through the gem. We can’t see images of what is beyond it.
A transparent gem is translucent and transmits light with little scattering. This allows us to see images as well as light through a transparent gem.
Opacity, Translucence, and Transparency
The more wavelengths of light a gemstone absorbs or reflects, the more opaque it is. (Both a solid black object and a mirror, for example, are considered to be opaque). The more light that is absorbed or reflected means there is less light to transmit through the gem.
A translucent gem can transmit enough wavelengths of light that we can see light shining through it. However, if the wavelengths of light that escape the gem are highly scattered, due to the gem’s refractive index (RI) or other physical properties, light is all we can see through the gem. We can’t see images of what is beyond it.
A transparent gem is translucent and transmits light with little scattering. This allows us to see images as well as light through a transparent gem.
Color - Agates have been found in a wide variety of colors. This is all due to the formation process with their original host rock. As the silica solution seeps into the volcanic rock cavities or fissures additional trace elements of minerals contaminate the solution. If the contaminating minerals are iron, then the solution will be tinted red. Various other elements will tint yellow, amber or even the world renown blue seam agates of Ellensburg, WA! The Washington coast tends to accumulate amber, white and yellow agates known as carnelian agates.
Banding - (concentric layering) - Agates are formed by the progressive depositing of silica solution into cavities and crevices inside of a host rock. This process of progressive deposition of silica solution produces a layering effect once the solution has hardened into solid rock. As these fragments of geodes or chalcedony wash down from the hills and are deposited onto beaches their distinctive characteristic is a visible area of banding or layering. An agate is defined as an agate if it illustrates banding. So, a careful agate hunter will also look for these characteristic lines embedded in the agate. The following gallery illustrates the types of agate banding that a beach comber might find.
Pitting - The illustrations below show the agate exterior is typically rough, pitted and ugly. It masks the beauty of the crystal inside. Many agates found on the beach illustrate a pitted surface texture. This reveals the the interior texture of the original host rock that the agate was born from. As I walk along a beach and explore the rock beds it is this "pitted" texture that also catches my eye and identifies the rock as an agate. There are also a few photos of narrow seam agates as they were found on the beach. These stones have experienced no processing and polishing in a rock tumbler to remove their original conditions as found on the beach.
The gallery below illustrates the moment of discovery for these agates and how they appeared on the beach. They are clearly distinct in coloration and texture as a beach comber scans the beach.
Orbicular Jasper - Agates may be moderately difficult to find but another rock is almost as challenging. Orbicular Jasper is a unique specimen of rock found in the Pacific Northwest. It is in the Jasper family of rock but presents a cluster of orbs over it's surface that are red in tone. Orbicular Jasper is a variety of jasper which contains variably-colored orbs or spherical inclusions or zones. In highly silicified rhyolite or tuff, quartz and feldspar crystallize in radial aggregates of needle-like crystals which provide the basis or seed for the orbicular structure seen in this kind of jasper. The material is quite attractive when polished and is used as an ornamental stone or gemstone.
This stone is unique to the Pacific Northwest and can be found as larger boulders in rivers further inland. It is, however, not as abundant as most rock found in rivers and on beaches. So, recognize it's rarity and enjoy the hunt. I have found Orbicular Jasper to be just about as rare as finding agates on on the beach. A few of my largest finds have come off of boulder covered beaches such as the Ediz Hook off Port Angeles, North Beach of Port Townsend, Murdock Beach west of Joyce and Rialto Beach out by LaPush, WA. My largest collection found in one day came off of Rialto Beach.
This stone is unique to the Pacific Northwest and can be found as larger boulders in rivers further inland. It is, however, not as abundant as most rock found in rivers and on beaches. So, recognize it's rarity and enjoy the hunt. I have found Orbicular Jasper to be just about as rare as finding agates on on the beach. A few of my largest finds have come off of boulder covered beaches such as the Ediz Hook off Port Angeles, North Beach of Port Townsend, Murdock Beach west of Joyce and Rialto Beach out by LaPush, WA. My largest collection found in one day came off of Rialto Beach.
Orbicular Jasper found on Rialto Beach, 4.4.16
Orbicular Jasper boulders found on Murdock Beach and Ediz Hook beach
Orbicular Jasper on Ediz Hook beach near Port Angeles, WA
Petrified Wood - One of the most rare finds that a beach comber can discover on a beach is that of a petrified piece of wood. A petrified fragment of wood tumbled in the surf is very difficult to identify and thus quite hidden from view. The average piece of petrified wood is not bright or translucent. It is always solid and very opaque with no light refracting through the stone. It is typically tan to gray in coloring which blends in with most other rocks found in a gravel bed. I have picked up only three pieces of surf tumbled petrified wood in my years of beach combing and they were all found on Damon Point beach at Ocean Shores, WA. I have probably walked past and over many petrified specimens without ever knowing it. The primary identifying characteristic of petrified wood is the consistent graining that flows in parallel lines across the stone. I will post pictures of each piece below for your examination.
Petrified wood found on Damon Point beach, Ocean Shores, WA