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stoanarrischer uhu

PostRank 11 / 11

Beiträge: 5360
Dabei seit: 12 / 2010

stoanarrischer uhu

22.08.2014 - 17:03 Uhr

· #1

Dear members,
today I send a puzzle with pictures of a "strange" mineral. Pictures are taken using daylight, neon tube 5000° Kelvin and incandescent light. What do You think about this rough and please give me reasons for.
Don't think the stoanarrische uhu got crazy totaly and excuse my English I learned about 60 years ago at school.
Please answer in English!
Uhu

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Sparkle

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Beiträge: 4104
Dabei seit: 11 / 2010

Sparkle

22.08.2014 - 18:31 Uhr

· #2

Ok, new thing in english, well You ask what we think? So, I´m a little bit astonished. The same piece looks first like saphire, then like tanzanite and at last like amethyst. But I also know that you kid us when we just go by the colour. And I think somebody had his hands on it. Edges look also like cutted/broken glass. Maybe I found a small piece of your puzzle? let us know!

stoanarrischer uhu

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Beiträge: 5360
Dabei seit: 12 / 2010

stoanarrischer uhu

22.08.2014 - 19:08 Uhr

· #3

In this case color is important. #1 and 4 are shot in daylight, when heaven was a little cloudy,
#6,7,8 with neon tube 5000°Kelvin and # 11 with incandescent light (tungsten). But look at the stripes or grooves cross to the crystal plane. This is typical for this mineral. The stone is a part of a cluster or geode. Can You find out the crystal system?
uhu

Bergkristall

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Beiträge: 1018
Dabei seit: 03 / 2012

Bergkristall

22.08.2014 - 19:09 Uhr

· #4

I think it is an Amethyst.

The shape of the cristal, the white area at the bottom and the twin-structure in picture 007 are signs that make me think this. And the piece has the typical signs for beeing grown close to other quartz-cristals. And the damage at the top points also in this direction.

Lis

stoanarrischer uhu

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Beiträge: 5360
Dabei seit: 12 / 2010

stoanarrischer uhu

22.08.2014 - 19:16 Uhr

· #5

Hallo Lis,
You are specialized and very familiar with quartzes. But are You sure?
uhu

Bergkristall

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Beiträge: 1018
Dabei seit: 03 / 2012

Bergkristall

22.08.2014 - 19:47 Uhr

· #6

Hi Uhu,

I don't like how high the white area ends, but I have a piece that is coveres by a white coating. Shure is, that this mineral is grown close to others, in kind of a geometric selection. You have written this. It has six crystal surfaces.

The stripes in picture 7 are no scratches on the surface? That's bad.

Lis

Frank Skielka

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Beiträge: 2231
Dabei seit: 04 / 2010

Frank Skielka

22.08.2014 - 20:41 Uhr

· #7

Changing the colour it could be a Chrysoberyl (Alexandrite).

Frank

Bergkristall

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Beiträge: 1018
Dabei seit: 03 / 2012

Bergkristall

22.08.2014 - 21:11 Uhr

· #8

When the change of colour the most important sign is, then it is a Saphire. Blue at daylight an violett at artifical light. This stones are found in Sri Lanka and Tansania.

And Saphire belongs to the trigonal System, same as Quartz.

Lis

stoanarrischer uhu

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Dabei seit: 12 / 2010

stoanarrischer uhu

22.08.2014 - 23:16 Uhr

· #9

Frank Skielka,
Alexandrite: blue in daylight?
uhu

stoanarrischer uhu

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Dabei seit: 12 / 2010

stoanarrischer uhu

22.08.2014 - 23:21 Uhr

· #10

Bergkristall,
do you think it's possible to test RI on a natural plane of this rough (on the top of the stone)?
uhu

Bergkristall

PostRank 11 / 11

Beiträge: 1018
Dabei seit: 03 / 2012

Bergkristall

22.08.2014 - 23:55 Uhr

· #11

Dear Uhu,

I don't work with refraction measuring. In the classical way I've had some problems with the Anderson liqiud and the other kind of measuring, the digital one, is to expensive für me. Especially because of my specialisation to the Quartz-family, I prefer microscoping.

By the way, in my last vacancies in Saxonia I found some nice pieces. mostly agates. I make some photos this weekend.

Lis

stoanarrischer uhu

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Beiträge: 5360
Dabei seit: 12 / 2010

stoanarrischer uhu

23.08.2014 - 08:11 Uhr

· #12

To all members:
The seller found a RI over 1,74 and a Mohs hardness of over 8. Does anybody know "andubon society field guide for rocks and minerals"? Accordant to this book color change of a mineral described like above identifies this stone as "Alexandrite". I found lower values of RI and Mohs hardness. The stone has about 13 ct wight. What do You think about now?
uhu

steinfroilein

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Dabei seit: 11 / 2012

steinfroilein

23.08.2014 - 08:19 Uhr

· #13

Dear Uhu, what a lovely puzzle.

My crystal of Amethyst with a weight of 494 grams is trigonal and looks like similar....

If having a plan side of crystal then a messuring of RI is possible.

RI 1.746-1,763, hardness 8-8,5 and changing colour would be Alexandrite.
But the crystal system is ortorhombisch. Birefringence and Dispersion of Chrysoberylle is higher than Quartz.