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 Post subject: Identifying Axis Orienting Titanite with Twinning plane.
PostPosted: Wed Oct 04, 2017 9:16 am 
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Joined: Wed Aug 09, 2017 8:33 pm
Posts: 80
Hello Everyone,
My first post here, I am obviously knew to the world of Gems but quite eager to learn, specifically about Faceting.
The issue at hand is related to crystals structure and how to identify their optical axis, and other axis as well as cleavage planes when none of the original crystal shape is present.

Case in point. There is this green sphene/titanite chunk which has been preformed into an hexagonal Shape. Even before it was preformed it was just a broken chunk with no discernable crystal shape. Can anyone help me find the axis' based on the information below?

As you can see in this rough drawing, the preformed is green overall, but different directions show me hue shifts between green and yellow. (love pleochroism btw)
There is an obvious twinning plane? It sits 1 third from the bottom up. Shows a strong orange color. I have drawn dotted lines to where I think the axis are; please correct me if I am wrong and clarify which one C A or B and the optic axis.
Axis (1) was meant to be the table, because I had read its best to have it perpendicular to the twinning plane. Unfortunately the color on the table would be the yellow and not the nice strong green seen on axis(3) Also, this Axis shows very obvious double refraction, as seen in the arrow on the drawing. There are plenty of inclusions and through the (1) axis they are visible doubled, one orange the other green. This would make the facets fuzzy and confusing no?

Too many questions :( please help. Tomorrow I can post some actual pictures of the preform.

Thank you in advance!


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 Post subject: Re: Identifying Axis Orienting Titanite with Twinning plane.
PostPosted: Thu Oct 05, 2017 6:14 am 
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Joined: Wed Aug 09, 2017 8:33 pm
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As promised, here are some actual pictures. First one represent the lower left from the diagram above. The second is from the lower right of the diagram.
I must say, Titanite is great, love it. It has such unique optical qualities but that is also what makes it quite a hard crystal to understand crystallographically speaking for the purposes of faceting.


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 Post subject: Re: Identifying Axis Orienting Titanite with Twinning plane.
PostPosted: Thu Oct 05, 2017 10:47 am 
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Joined: Thu Jun 03, 2010 1:49 pm
Posts: 331
Location: South Africa
A good start for finding the optic axis is to use a polariscope.
Very easy to make and use.


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 Post subject: Re: Identifying Axis Orienting Titanite with Twinning plane.
PostPosted: Thu Oct 05, 2017 3:48 pm 
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Joined: Wed Aug 09, 2017 8:33 pm
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Yes I need to start getting me some instruments. I was hoping however, if i could figure out axes based on the optical qualities (mainly color pleochroic color and twining) then i could figure out the orientation of the crystal structure and end up knowing the rest of the info.


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