rocpup
spending too much on rocks
Pink Limb Iris
Member since March 2011
Posts: 465
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Post by rocpup on Aug 15, 2012 22:03:39 GMT -5
Hooked on Iris In 1963 on a gravel bar along the Chehalis River in Western Washington I picked up a agate nodule about 2x2 inches and weighed about a half pound. The agate had some nice banding and color that needed cut. My saw in those days was a ten inch Craftsman horizontal all in one machine. The rock would just fit the vise and a couple of hours I had a couple of nice ¼ inch slabs. One of the slabs was turned into two 18x13 and one 30x20 cabs. I showed them to a old rockhound. He held them up to the light and said there was a rainbow showing and it was called Iris. He told me I needed to cut a thin slice and polish both sides. That was not an easy task with the flat machine. The first slice was cracked from excessive heat but what a beauty. The second slice I remember took over eight hours to polish. Needless to say few people have touched it over the years. The cracked slice was passed around for show and tell. It was dropped and glued back together. For the next few years there was many hours spent looking and cutting agate from gravel bars along the river and I never found another Iris from there. I now have a large collection of near 300 pieces with few of them polished.
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rocpup
spending too much on rocks
Pink Limb Iris
Member since March 2011
Posts: 465
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Post by rocpup on Aug 15, 2012 22:10:48 GMT -5
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rocpup
spending too much on rocks
Pink Limb Iris
Member since March 2011
Posts: 465
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Post by rocpup on Aug 15, 2012 22:11:27 GMT -5
I did a little research a couple of years ago for a Rock Club presentation. I don’t know if it belongs here but it may help a little to understand Iris Agate.
Iris a play of Color
“The chemical compound SiO2 or silicon dioxide, also known as silica, is a oxide of silicon and is known for its hardness and durability. Silica is most commonly found in nature as sand, quartz or agate. It is a principal component of most types of glass and concrete. Silica is the most abundant mineral in the earth’s crust.
Agate is a microcrystalline variety of quartz , chiefly chalcedony, characterized by its fineness of grain and vast variety of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks.
The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone in Sicily along the shore line of the river Achates (spelling) sometime between the 4th and 3rd centuries BC. This collected mineral has been recovered at a number of ancient sites, indicating its widespread use in the ancient world. For example spear points, arrow heads and assorted other tools made of agate are found at once inhabited sites of some 50000 plus years ago.
Many agates occur as nodules or veins in volcanic rocks or lavas where they represent the gas pockets, or cracks caused by shrinkage from cooling. The originally produced gas pockets in the molten mass were then filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls. Such agates, when cut across the grain, exhibit a succession of parallel lines, often of extreme closeness, giving a banded appearance to the cut. This very fine banding is what we are getting to here.
In the formation of an ordinary agate, it is probable that waters containing silica in solution -- derived, perhaps, from the decomposition of some of the silicates in the lava itself -- percolated through the rock and deposited a siliceous coating on the interior of the cavities or shrinkage cracks. Variation of suspended chemicals in the solution may cause a variation in the successive layers, so that bands of chalcedony often alternate with layers of crystalline quartz. Many agates are hollow, since deposition has not proceeded far enough to fill the cavity, and in such cases the last deposit commonly consists of quartz, having the points of the crystals directed towards the free space so as to form a crystal-lined cavity, or a geode.
After the erosion of the volcanic rock hills and mountains in which the agates are embedded, they are set free. The agates are extremely resistant to weathering and remain as nodules in the soil or are deposited as gravel in streams and shorelines.
Iris according to Webster means: rainbow show or a play of color. We can extend that meaning to a favorite of mine Iris Agate.
Many rock and gem enthusiasts profess a weakness for iris agates. You can often spot iris agate fanciers at gem and mineral shows. We poke around agate booths, holding up slices to light with the hope of finding the ultimate iris agate for their collections. At Quartzsite we have spent hours looking through slabs at the gem shows. Inevitably, we buy any agate that exhibits iris, even small bands that show signs of color. The problem of iris agate slices is that they must be backlit so their phenomena can be seen. Often drab in appearance in reflected light, these agates are transformed into the full color spectrum when you shine a strong light through them.
Many iris agates are missed when looking for them at gem shows because they are stored in water. For whatever reason water will not show the rainbow effect and the lighting has to be from a single source like maybe the sun. The slabs from Brazil are polished but are near a ¼ inch thick but you can find great collectibles. Most of the time we are very quiet about what we are looking for. Most of the people think we are just looking for pretty slices but we are looking for the prize.
If you have a rock saw and have not looked in your rock pile here are a few hints. Look for clear nodules. Much of the iris I have found came from agate that would be discarded because it did not have enough interesting inclusions. The pink limb casts from Oregon are great places to look. The pink color does not hold up when cabbed so the cut pieces are just polished and admired. Maybe they have hidden color. OK you have a clear agate and you put it in your saw. If it is a partial nodule cut it across the grain and not with it. After the first cut set your saw to cut another slice about 1/16 of an inch thick. After the second cut take the thin slice and clean it with soap and water. Dry it and now for the magic. If held to the light with saw oil or water the iris does not show well but a few drops of 3 in one oil or olive oil and hold it up to the light. If it is iris jump up and down with glee because the next 50 may not be. I have kissed a lot of frogs. Thin slices of clear agates may exhibit a vivid play of colors when viewed in light from a small bright source. I have found a clear not frosted incondesant light bulb of about 25-40 watts works just fine. The colors are caused by a very fine agate banding, that acts as a diffraction grating on the light . The observed colors change with the viewing angle. The strongest effect is seen in slices of less than 1/16 inch thickness that were cut perpendicular to the banding (just as most agates are cut to show their regular banding). Experts say a form of diffraction grating causes the phenomenon. The grating is made of alternate layers of slightly higher and lower refractive index that run parallel to the regular bands. Bands in agates can be so close together (up to 10,000 bands /cm or 250,000 /inch), the distance between them can be similar to the wavelength of light. In Iris agate the bands act as a diffraction grating, enhancing certain wavelengths and suppressing others thus exhibiting all colors of the spectrum. Very fine parallel lines of an exact spacing in the agate’s structure, each with different refractive index, cause the rainbow effect.
When I did a little research on this the words got very complicated very fast.
Iris agates have been found in many places but not all. When you find one chances you will find more from the same area. The place to start looking is in clear agate nodules. I have been told or maybe read that your chances are about 2000 to one of finding one but I have found that the odds for me are much better than that maybe 50 to one. I think my odds are better because I am aware of what type of agate I have found iris in.
When most of rockhounds are out picking up rock we tend to bring everything we find home. Then high grade, the clear stuff is placed in the reject pile. When you look at my discard pile you will find all the clear ones have been cut. Hmm I wonder why.”
Don Hixson
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itsandbits
freely admits to licking rocks
Member since March 2012
Posts: 825
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Post by itsandbits on Aug 16, 2012 12:15:49 GMT -5
amazing, never ran into this before myself but a new clear cutter is born; and I don't mean trees: it's called clear cutting when forestry cuts down all the timber in a particular section of property. Ugly but effective for profit.
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Post by gingerkid on Aug 16, 2012 12:25:03 GMT -5
Holy smokes, those are beautiful! You have 300 pieces of iris agate, rocpup?!! Really like the one with the dendrites in it, cool!!
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Post by parfive on Aug 16, 2012 21:36:45 GMT -5
Pics wouldn’t open last night, Don, but I can see them now.
Some very nice shots and some sweet iris!!
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Post by roy on Aug 16, 2012 23:06:23 GMT -5
wow look at those ! thats way cool
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Post by helens on Aug 17, 2012 20:54:09 GMT -5
WOWWWW!
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