CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: Re: What crystal form is this?
PostPosted: Wed Apr 27, 2011 7:28 pm 
Yes indeedy. Very helpful. Just one more question in regard to the Table Cut before diamond saws. But tomorrow.... I need some sleep.....


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 Post subject: Re: What crystal form is this?
PostPosted: Thu Apr 28, 2011 1:28 pm 
Tim wrote:
Quote:
Yet the only octohedral piece of Fluorite I have as all its planes, well, as clear as crystal


most octahedral bits of fluorite you'll see are the product of cleaving... that would explain your 'clear' faces...


Tim,
I forgot that I actually have two. One is very decreipt but may help here. To my knowledge, I've never (yet) seen a stone face that has been deliberately cleaved and have no source of reference that shows the tell-tale differences, if any, between a man-made cleavage and an act of nature. I imagine that of the two below, the red stone at least can be relied on to have its natural form:

1. What once was an octahedral red Fluorite and is now badly eroded anand otherwise knocked about. Even so, where they still exist, the planes are smooth and with a glassy lustre.

Attachment:
Fluorite 1-01b.JPG
Fluorite 1-01b.JPG [ 105.22 KiB | Viewed 1425 times ]

Attachment:
Fluorite 1-04b.JPG
Fluorite 1-04b.JPG [ 122.84 KiB | Viewed 1425 times ]


2. My clear octahedral specimen. I had thought that the growth related markings shown on this pic, including a trigon, might assure that the planes were naturally formed. Smooth and glassy too.
Attachment:
Fluorite 2-03b.JPG
Fluorite 2-03b.JPG [ 108.39 KiB | Viewed 1425 times ]


What do you think, natural planes or...?


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 Post subject: Re: What crystal form is this?
PostPosted: Thu Apr 28, 2011 1:54 pm 
Tim wrote:
Quote:
OK... As I understand it, to cut a Table Facet diamond, one of the ancient cutters would cleave the point off an octahedral Diamond crystal, parallel to the crystal's natural girdle, creating a tetragonal table by that process. Is that correct?


nope



Thanks. That was instructive (the vid). How the Table Cut came to be the first know diamond cut can wait, I think.


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 Post subject: Re: What crystal form is this?
PostPosted: Thu Apr 28, 2011 2:28 pm 
Tim wrote:
'BTW...

Where exactly do you see that cleavage? (cuz i don't see any... ).


Try this one? It's easy to see in the hand but is a devil to photograph :cry:
Attachment:
Fluorite 3-07b.JPG
Fluorite 3-07b.JPG [ 101.08 KiB | Viewed 1418 times ]
.
It's like a mirror, reflecting light to the right. It does not reach the surfaces of the stone nearest to the camera,


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 Post subject: Re: What crystal form is this?
PostPosted: Thu Apr 28, 2011 2:44 pm 
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Fantasic video Tim.


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 Post subject: Re: What crystal form is this?
PostPosted: Thu Apr 28, 2011 2:51 pm 
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Kerensky wrote:
Tim wrote:
'BTW...

Where exactly do you see that cleavage? (cuz i don't see any... ).


Try this one? It's easy to see in the hand but is a devil to photograph :cry:
Attachment:
Fluorite 3-07b.JPG
.
It's like a mirror, reflecting light to the right. It does not reach the surfaces of the stone nearest to the camera,


BS Owen... you thought that cubic face was the product of cleaving.

re: those other pics, what do you think yourself, does any of those faces look like a cleavage plane to you?


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 Post subject: Re: What crystal form is this?
PostPosted: Thu Apr 28, 2011 3:58 pm 
Tim wrote:
Kerensky wrote:
Tim wrote:
'BTW...

Where exactly do you see that cleavage? (cuz i don't see any... ).


Try this one? It's easy to see in the hand but is a devil to photograph :cry:
Attachment:
Fluorite 3-07b.JPG
.
It's like a mirror, reflecting light to the right. It does not reach the surfaces of the stone nearest to the camera,


BS Owen... you thought that cubic face was the product of cleaving.

re: those other pics, what do you think yourself, does any of those faces look like a cleavage plane to you?


Re cubic underface (only a strip exposed) . Yes I did. And thanks for the instruction. I also at the time mentioned the other one, now pictured.

Re. octahedral crystals. As I said, I have no known basis of comparison, which is why I asked *you*. My guess by observation is that they are both naturally formed shapes and sizes and have (or once had) 'smooth' not 'rough' surfaces.


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