Post subject: My finding: Sarawak amber from various geological formations
Posted: Wed Dec 30, 2015 12:26 pm
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Joined: Tue Dec 14, 2010 2:10 am Posts: 44
Hi, Here is the amber I found recently in Mukah roadcut area, Sarawak, Malaysia. Liang formation, Plio-Pleistocene age. The amber situated in ~2 million years old strata. Which is extremely young for normal amber. They pass the acetone test and crazing free.
That's really interesting. I had thought that Sarawak amber was found in veins in coal seams, but it looks like you're pulling it out of shale. I wonder if it's a secondary deposit, chunks that floated away and were (somehow) mixed in with deposited sediments.
Post subject: Re: My finding: Sarawak amber from various geological format
Posted: Wed Dec 30, 2015 1:03 pm
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Joined: Tue Dec 14, 2010 2:10 am Posts: 44
Perhaps they redeposited at shallow marine shale during Early Pleistocene high sea level. Original source of these amber came from Plio-Pleistocene thick lignite seam at that area too. So, I can only assumed that amber 2-3 million years old.
Post subject: Re: My finding: Sarawak amber from various geological format
Posted: Wed Dec 30, 2015 1:11 pm
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Joined: Tue Dec 14, 2010 2:10 am Posts: 44
Begrih formation, slightly older, Lower Pliocene about 4 million years old...these amber came directly from lignite seams. Most are very brittle but a few of them can be cut as organic gems.
As a side-note, this stuff hit Tucson pretty hard last year, and I picked up a few pounds of smaller pieces from a friend of mine. A lot of it was being sold as Indonesian but one of the dealers said it was actually Malaysian. I've had pretty good luck with the pieces I've worked with, though I suspect your pieces are probably of higher quality since they've already proved they can survive under difficult conditions. Anyway, it's really beautiful stuff. No bugs in any I've looked at so far but hope springs eternal.
Post subject: Re: My finding: Sarawak amber from various geological format
Posted: Sat Jan 02, 2016 4:21 am
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Joined: Tue Dec 14, 2010 2:10 am Posts: 44
Usambara effect usually occurs in crystalline gems like some tourmaline etc. Depends on the light path through the material. I don't know if amorphous material do have usambara effect too...
Post subject: Re: My finding: Sarawak amber from various geological format
Posted: Sat Jan 02, 2016 12:03 pm
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Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
There seem to be some who have documented usambara in amber. I am not one of them. But I believe that this phenomena was originally called "color shift" in an article discussing garnets. I know one of us will find a link for you.
Post subject: Re: My finding: Sarawak amber from various geological format
Posted: Sat Jan 02, 2016 4:08 pm
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Joined: Mon Apr 16, 2007 12:05 am Posts: 1499
Iskandarman wrote:
Usambara effect usually occurs in crystalline gems like some tourmaline etc. Depends on the light path through the material. I don't know if amorphous material do have usambara effect too...
I feel like practically every transparent orange-red material is going to look yellow or amber when cut thin. It's such a ubiquitous phenomenon it seems strange for them to even comment on it--no doubt it has origins similar to a proper usumbara with regards to relative perception of red and yellow color components at different levels, but unlike a red/green change it's not unfamiliar or particularly interesting.
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