Joined: Sun Jul 09, 2006 11:19 am Posts: 273 Location: Michigan & Arizona
Hi all,
Haven't had a chance to post photos of some of the noteworthy stones I have come across since Tucson. I did a "finds" thread last year and wanted to get around to something similar. Since I was doing photos today anyway, I though I might as well get started!
First up is...
One of the nicest examples of gem Cassiterite that I can recall seeing. Loupe clean and with the mineral's typically high luster. Visually, it resembles a nice Pakistani Sphene. The first day in Tucson and I was smitten with it - one of those things that if you don't sell, then oh well!
Joined: Sun Jul 09, 2006 11:19 am Posts: 273 Location: Michigan & Arizona
Up next is a piece of inclusion Quartz. There is such variety in this area that it is becoming more and more popular each year.
This ~70ct. Brazilian piece includes Tourmaline, Mica and several others yet unidentified. I try not too get too wild in my interpretation of these, but it seems almost like an underwater scene.
Joined: Sun Jul 09, 2006 11:19 am Posts: 273 Location: Michigan & Arizona
Next up is a rare example of magnesio-axinite from Merelani, Tanzania. The color(s) are not what we would expect from typical gem Axinite and there is in fact a distinct color change.
This material is mined along with Tanzanite and I saw several rough pieces which actually contained Axinite and Tanzanite. Most of it tends to be specimen or cab grade at best.
Joined: Sun Jul 09, 2006 11:19 am Posts: 273 Location: Michigan & Arizona
Thanks Barbra. I may be out your way to do some shows later this year, so I will issue a standing invitation! I need to get a few more photos taken and will post some more here.
Nice stone and I'm sure you don't take this as an attack, but maybe we should start a good discussion on colour change and colour shift one day again. I don't think this stone (from the images) would qualify as "colour change".
I remember an article in G&G a while ago which made a distinction between colour change and shift based on transmitted/reflective light .. I lost the link to that article though. According to that article this stone would also not validate a "colour shift" qualification.
A few months ago I went to the pearl exhibit in Paris and my lovely companion witnessed the change of colour on the catalog cover when looking at it from different angles while exposed to the same light source.
I think a good discussion on this topic is needed.
_________________ Proud to be a DSN and JTV shopper, just love the guys!
Joined: Sun Jul 09, 2006 11:19 am Posts: 273 Location: Michigan & Arizona
Hi Doos,
No offense taken at all. I debated whether or not to say this as I thought this may come up. My first choice would have been to use "color shift" but then I thought that this may even be more provocative as some don't like that term.
In the most recent G&G (Winter 2007) they describe this material using the term "subtle color shift". I would have to reference the specific article you mentioned, but this material apparently does qualify.
While commuting a while ago I had the time to read up on some articles regarding this topic and they recommended a change of at least 20 degrees on the CIELAB colour wheel for a stone to qualify as a colour changing stone. Although that was just a recommendation.
I'll find the appropriate articles for you, they were from the DgemG.
_________________ Proud to be a DSN and JTV shopper, just love the guys!
Joined: Sun Jul 09, 2006 11:19 am Posts: 273 Location: Michigan & Arizona
Next up is a nice example of Amethyst from the Jackson's Crossroads locality in Georgia. While not as unusual a material as I usually post, I am consistenly impressed with the finished goods from this site.
This example weighs just under 9 carats - fairly large for these.
I had some trouble finding the articles because they were not published in the German Gemmologie but in the JofG.
"A colorimetric study of the alexandrite effect in gemstones" by Liu, Shigley, Fritsch and Hempill.
"Colour hue change of a gem tourmaline from the Umba Valey, Tanzania" by Liu, Shigley and Halvorson.
Both articles published in the JofG, Vol. 26, No.6, April 1999 (PP. 371-397).
_________________ Proud to be a DSN and JTV shopper, just love the guys!
Up next is a piece of inclusion Quartz. There is such variety in this area that it is becoming more and more popular each year.
This ~70ct. Brazilian piece includes Tourmaline, Mica and several others yet unidentified. I try not too get too wild in my interpretation of these, but it seems almost like an underwater scene.
Brad,
I gotta say that I gotta get some of this stuff! I like your interpretation. I have some rather abstract "underwater scene" paperweights - my favorites. Before I read, I saw the pic (wow, imagine that). My immediate impression was the same - underwater scene.
Seeing your collection would be an extreme delight.
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