This rock has been in storage for over 40 years. I tried to do some research. It looked similar to blue lace agate? As you can see, it has a shade of light blue in it, but when you hold a light to it ( a regular white household light bulb), it changes to an amber color. It's translucent from the center going to the outer edges. I would appreciate any thoughts about it, and if anyone know what kind of rock it is. Also, it's at least 8" X 8" X 2". Thank you!
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Is this Blue Lace Agate or something else?
- Thread starter rockby
- Start date
First off you would be better served if you move this to the Rock and Mineral Forum. Second, what is the light source for the blue? And exactly what bulb are you using that turns it yellow? Some minerals will change color depending on light source but this is a mystery to me so far.
Hi and thank you for the response! I'm new to this website, so will have to figure out how to move this to the proper rock and mineral forum. The lighting was just a regular 60v household lamp light bulb. I will try some different lighting sources, and see the results. It is a mystery. Thank you for taking the time and have a great day!
mystery to me too. I spent some time trying to find this light change in other minerals and there are very few that do it, except if using ultraviolet lights. Agate was not one of them under various white light sources. If this was some unique thing I would think the mineral collectors would be all over it and there would be postings on it. I found none. it could be that someone dyed it but I would expect to see some of the dye remnants on the chert matrix and it's the dye that's changing color. White light does have different wave lengths. The center is quartz. Now that's a long way of saying "I have no idea". 
Hi again! Thank you very much for taking the time to research this, and shed some light on this. Someone suggested this could be an agate nodule cross section. One more interesting discovery about this piece. The blue outline is slightly different in shape on each side of the rock. Additionally, this piece is heavy, about 7-8 lb. The light goes through the rock on each side perfectly. I held it in the light. I don't see anything that looks unnatural. Again, thank you! I really appreciate it!
p.s. As I said, this was stored in a box for over 40 years in a barn in the upper midwest, U.S.A.. There were some other rocks. I'll try to upload pictures. Maybe that will give us some clues at least maybe for the region that they came from. Here's one blue one.
p.s. As I said, this was stored in a box for over 40 years in a barn in the upper midwest, U.S.A.. There were some other rocks. I'll try to upload pictures. Maybe that will give us some clues at least maybe for the region that they came from. Here's one blue one.
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Picketwire
Well-known member
Maybe Geologyhound can shed some light on the subject. That is one beautiful rock! Nice photography too!
Thank you for the compliment! Maybe Geologyhound is enjoying the 4th of July holiday? Hope he can shed some light. Again, thank you!
p.s. here is another rock that was in the collection, which I have no clue what it is.
p.s. here is another rock that was in the collection, which I have no clue what it is.
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the last pics you posted seem to look like Calcedony. As to your first pics I found this on GemSelect.com. " Some gemstones show a distinct or dramatic change in color under different light sources. Look at a garnet under electric or artificial light and it could look red, take it outside into the sunlight and all of a sudden it is green! This remarkable effect only occurs in a few gemstones, Alexandrite, Garnet and some Sapphires being the most well known but does NOT occur in agates."
Hi Johnho! Thank you very much for digging more into this topic. It's much appreciated! So, if I understand you...it may not be agate because of the color changing property it has....and it could be something else like the above named gemstones. I visited the website you mentioned above. I saw where they talked about the color changing properties in some of these stones. That was very helpful. I hope one day I figure out what it is. Again, thanks so much!
Geologyhound
Well-known member
My ears were burning so I thought I would check in….
it has been a busy last week and I haven’t had much chance to frequent the forums.
First off, I always love blue and purple agates, and it looks like you have some nice specimens. My knee-jerk reaction is blue fortification agate with quartz crystal center. Color change of rocks can be a little tricky. I am guessing you used transmitted light rather than reflected light? In other words you held the sample up and let light shine through it rather than set it on a neutral surface and let light reflect off of it to obtain the color change, correct? If so, I would say blue fortification agate. It is not “lacy” enough to be a lace agate in my mind.
Also, blue agates are subject to Tyndall Effect scattering of transmitted light which would result in a yellow/orange color. Note that the quartz crystals in the center were not as strongly yellow under transmitted light. That would also stand to reason as the size of the particle scattering the light is important and varies between chalcedony and quartz. If you have a black light see if it turns green. That would be another indicator for blue chalcedony.
Hard to tell in the pictures, but I am guessing the host rock may be white rhyolite. That doesn’t match with what little I can find for the descriptions of the typical Pacific Northwest sources (Ellensburg Washington, Holly Oregon, or Madison Montana). I have some Holly and a couple pieces of Ellensburg, but nothing like that. So, I am not sure of the source area. Shipping has been around for a while so it could literally be from anywhere in the world if only stored for 40 years. However, the other pictures you show do appear to be from different locales, so I think this is a collection from multiple locations.
The host rock on the first picture appears to be more of a larger nodule or thunderegg type morphology. There are many locales near Prineville Oregon with a variety of thundereggs of varying types. I have even found thundereggs in road cuts. So it could be from an unknown locale. But, a locale with something that nice should’ve been claimed. The other samples could be from a ledge agate locale.
it has been a busy last week and I haven’t had much chance to frequent the forums.First off, I always love blue and purple agates, and it looks like you have some nice specimens. My knee-jerk reaction is blue fortification agate with quartz crystal center. Color change of rocks can be a little tricky. I am guessing you used transmitted light rather than reflected light? In other words you held the sample up and let light shine through it rather than set it on a neutral surface and let light reflect off of it to obtain the color change, correct? If so, I would say blue fortification agate. It is not “lacy” enough to be a lace agate in my mind.
Also, blue agates are subject to Tyndall Effect scattering of transmitted light which would result in a yellow/orange color. Note that the quartz crystals in the center were not as strongly yellow under transmitted light. That would also stand to reason as the size of the particle scattering the light is important and varies between chalcedony and quartz. If you have a black light see if it turns green. That would be another indicator for blue chalcedony.
Hard to tell in the pictures, but I am guessing the host rock may be white rhyolite. That doesn’t match with what little I can find for the descriptions of the typical Pacific Northwest sources (Ellensburg Washington, Holly Oregon, or Madison Montana). I have some Holly and a couple pieces of Ellensburg, but nothing like that. So, I am not sure of the source area. Shipping has been around for a while so it could literally be from anywhere in the world if only stored for 40 years. However, the other pictures you show do appear to be from different locales, so I think this is a collection from multiple locations.
The host rock on the first picture appears to be more of a larger nodule or thunderegg type morphology. There are many locales near Prineville Oregon with a variety of thundereggs of varying types. I have even found thundereggs in road cuts. So it could be from an unknown locale. But, a locale with something that nice should’ve been claimed. The other samples could be from a ledge agate locale.