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Offline wildhorse

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Help identifying this strange stone
« on: 31/12/2010 10:03:27 »
Hello, can someone identify this strange stone, it's heart shaped found in the Egyptian western desert, the core looks semi-transparent orange-red against the light but almost black in normal light with a thin dim multicolored layer on most of the surface with strange shapes.

Photos showing it in normal light and against the sun.









 

Offline RD

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« Reply #1 on: 31/12/2010 13:59:23 »
Maybe a tektite ? ...

Quote
Tektites are usually translucent and occur in a range of colors from green to brown. Their surfaces are usually uneven or rough, with a distinctive lumpy, jagged, or scarred texture. Tektites do not contain the crystallites found in obsidian. They may, however, have characteristic inclusions of round or torpedo-shaped bubbles or honeylike swirls.
http://en.wikipedia.org/wiki/Tektite

http://www.tektites.co.uk/veryquickguide.html

The concentric features are intriguing, (eruption?, mini-impact?)





I was going to suggest mahogany obsidian, but it looks like the black bits are only on the surface, (fusion crust ?). 

« Last Edit: 31/12/2010 15:47:54 by RD »
 

Offline RD

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« Reply #2 on: 31/12/2010 22:02:11 »
... found in the Egyptian western desert

Libyan Desert Glass [Tektite], Area, Great Sand Sea, Western Desert, Egypt ... http://www.mindat.org/gallery.php?min=10859&loc=105744

also see ... http://www.tektites.co.uk/libyan-desert-glass.html

Quote
tektite (from the Greek tektos,  meaning molten), a natural black, dark green, or dark brown glassy stone, resembling the volcanic glass obsidian, that may possibly be of extraterrestrial or meteoritic origin. Tektites, which occur in four large associations of distinctly different ages throughout the world known as strewn fields, are similar to Libyan Desert glass in that both substances are composed chiefly of silica (silicon dioxide); the silica content of tektites ranges from 68-80 percent whereas that of Libyan Desert glass is approximately 98 percent. Both tektites and Libyan Desert glass are characterized by etched, pitted surfaces, which in the case of some of the silica glass may have been obscured by the scouring action of the fierce Saharan winds.
http://www.saudiaramcoworld.com/issue/197905/desert.glass-an.enigma.htm

« Last Edit: 31/12/2010 22:30:24 by RD »
 

Offline wildhorse

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Help identifying this strange stone
« Reply #3 on: 01/01/2011 09:50:39 »
Thank you MD for your reply, from the info you included this must be Tektite

Here's 2 other rocks from the same location but they are different, the dark one is dim with only the whitish part semi-transparent against the light but they are like melted together. The white stone is transparent, both are smooth and don't have outer crust







The concentric features are intriguing, (eruption?, mini-impact?)





Any ideas what is the outer layer? it's like crust and the inside is clear when you turn it against the light here's another closeup :



 

Offline RD

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« Reply #4 on: 01/01/2011 15:28:06 »
... from the info you included this must be Tektite

I wouldn't go as far as "must be", you could try showing a picture of the heart shaped thing to a tektite expert, e.g. on this page

Any ideas what is the outer layer? it's like crust and the inside is clear when you turn it against the light

Tektites are glass: sand melted by a large meteor impact and ejected into the atmosphere.
The black outer layer is "fusion crust" where it was charred by air friction when it re-entered the atmosphere,
 i.e. in your case a thin layer of dark-coloured glass over clear glass.

BTW some consider clear Libyan desert glass is impactite rather than tektite.
« Last Edit: 01/01/2011 15:47:07 by RD »
 

Offline wildhorse

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« Reply #5 on: 01/01/2011 15:59:32 »
Thank you for the contact link, I will do that.

Also thanks to your links that provided interesting reading for a beginner like me; I'm also not sure now.. after Google image search for "Libyan Desert Glass" it doesn't look like any of the many photos there in color or shape, but I'm sure now that some other rocks I have from the area are Libyan Desert Glass.

And actually maybe the photos was a bit misleading, what looks "black" in normal light is the clear reddish core that shines against the light; while what looks bright colored with the concentric shapes in normal light is the dim crust that looks about one millimeter thick on the surface when you turn the stone against the light.. So the outer layer is not black.

I hope my description is clearer this time.
 
 

Offline RD

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« Reply #6 on: 01/01/2011 21:43:14 »
Another tektite-ologist :) worth showing the pictures to at the bottom of this page 
 

Offline aubreywhymark

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« Reply #7 on: 02/01/2011 08:37:37 »
Hi

Refering to the first posted stone (others are unrelated). I am the author of newbielink:http://www.tektites.co.uk [nonactive]. I can 100% guarantee this is not a tektite, impactite or meteorite - this rock is wholly terrestrial in origin. Tektites are glass, this clearly has structure. Libyan desert glass may have round cristobalite inclusions, but nothing like this - This is not LDG. I am a qualified geologist (oil industry) and I would suggest from the photos that this is a pisolite which may have undergone metasomatic alteration, probably enriched in iron. Pisoids are like large ooids. Do a google image search for 'Pisolite' and 'Pisolitic'. The rock was reportedly found in the Western desert of Egypt so you need to research the geology in the area with reference to Pisolites.

Regards, Aubrey Whymark
 

Offline JimBob

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« Reply #8 on: 04/01/2011 04:27:57 »
The perfectly circular features range from very faint to very bold. I would think they MUST be some type of fossil.

At first glance it looked like crinoid "hash." Then I saw it was somewhat translucent. Still looks like crinoid "hash."

Then you had to go post your clearer description.

That complicates things. The rock could be just a type of quartz with a strange type of desert pavement on it. (This would be the orange brown colored stuff. )

Yet nether of these seem plausible geologically.

When Bass gets back from his New Years travels and can add his opinions and I hopefully begin to recover from this latest bout of crud-in-the-lungs, I will hopefulness have a clearer view on this conundrum.
 

Offline wildhorse

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« Reply #9 on: 04/01/2011 08:14:57 »
Thank you all guys for your help, it seems it's easier to know what it's not than what it is!

Thanks RD for directing me to where to start.

In email conversation Aubrey Whymark thinks it's also not an Agate; but I'm in contact with an Agate expert now and I hope to know for sure about this possibility..

JimBob, waiting for more input from you.

Happy new year for all :)
 

Offline Bass

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« Reply #10 on: 07/01/2011 00:52:45 »
I agree with JimBob- circular features are some type of fossil.  Whatever it is seems to be enmeshed in cryptocrystalline quartz (agate, jasper, chalcedony). 

Other rocks appear to be quartzites
 

Offline wildhorse

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« Reply #11 on: 10/01/2011 08:53:30 »
I got 2 replies from agates experts/collectors saying practically the same thing so I'm satisfied with calling it an agate.

In case anyone is curious here are the 2 opinions, I'm not posting the names since our conversations were in private emails and they could have posted here if they wanted to.

1:
If you cannot see through the agate, we call it jasper.  Often the two are mixed together.  Rock hounds have lose unscientific terms when describing material.  Jasper and agate are sometimes called jaspagate.  To say that your specimen is jasper and agate is more correct. The eyes are often banded and form around random nuclei.  They are a kind of orb.  When we find orbs in jasper we call it orbicular jasper. Orbs are normally smaller than a centimeter.   It may be there is a layer of manganese or iron oxide where the eyes are that is keeping you from seeing through the specimen where the eyes are.  You would likely have to cut it to determine that.  I don't know if you want to do that.

2:
I can tell that it has been naturally tumbled in an ancient river that once ran through western Egypt and then wind-polished.
      The fact that it's clear inside gave it away as an agate and the "rings" you see on it is more common in agates than any other stones. The golden layer is a result of weathering where the iron pigments on surface are altered, becoming more yellowish. The inside should bereddish-brownish. Agates had been found in Algeria also.

Thanks to all who contributed to this thread

 

Offline JimBob

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« Reply #12 on: 11/01/2011 05:03:48 »
I must disagree with the jasper-agate expert. This is NOT orbicular Jasper. I do agree with the diagnosis of translucent agate with desert pavement weathering. The round things, however, can only be fossils of some nature. Agatized crinoid stems pieces, foramanifera or fussilinids. These have been weathered out on the surface, as seen in the close-up of the enlargement RD made, are not part of either colored agate-jasper. 
 

Offline RD

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« Reply #13 on: 11/01/2011 05:32:24 »
The pendant inserted in the image is described (by the jeweler) as "fossils in agate" ...


http://www.sevilladesigns.com/jewelryzoom

The features with concentric circles do look similar to those on the heart shaped find.

« Last Edit: 11/01/2011 05:51:25 by RD »
 

Offline RD

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« Reply #14 on: 11/01/2011 06:15:22 »
The flower-like thing is a fossil coral, on the right is a monochrome image of a circle on the heart shaped find ...



I'm not suggesting they are exactly the same type of fossil, just that the circles are similar.
« Last Edit: 11/01/2011 07:54:33 by RD »
 

Offline JimBob

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« Reply #15 on: 12/01/2011 03:21:54 »
Very astute RD. The jasper is replacement of a carbonate if these are corals. Replacement of the entire matrix has been noted in many places in the geology of the earth.
 

Offline wildhorse

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« Reply #16 on: 13/01/2011 09:06:06 »
I did more search, reading and looking at photos online; and it seems that fossil in agate/ jasper is not a rare thing.

So far I understand how agates and fossils form; but I thought fossils should be embedded in the rock not forming around its surface or "enmeshed" as "Bass" put it.. samples I see online seems to be described as "enclosures" . So I hope someone can explain to me some more or post a theory about how it was formed, thanks
 

Offline Mazurka

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« Reply #17 on: 13/01/2011 10:12:38 »
Agates are a very fine grained quartz.

Subsequent to initial fossiliation, sillica rich (hydrothermal) ground water will have replaced the calcium carbonate/ phosphate of the fossil.   

http://www.ehow.co.uk/list_6385741_types-body-fossils.html

is a reasonable discussion in plainish language about this.

 

Offline RD

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« Reply #18 on: 18/01/2011 07:03:09 »
 

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