CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: Idiochromaticity—if that's a word.
PostPosted: Thu Jul 26, 2007 1:33 pm 
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My dictionary gives the following definitions:

Allochromatic - a (mineral) having no color in itself but bearing colored impurities.

Idiochromatic - a (mineral) deriving a characteristic color from its capacity to absorb certain light rays.

My question is, “Which of the following gemstones are idiochromatic?”

Peridot
Ruby
Rhodolite
Amethyst
Tsavorite
Rhodochrosite


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PostPosted: Thu Jul 26, 2007 1:43 pm 
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Hi,

Following that definition, I would say all.


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PostPosted: Thu Jul 26, 2007 3:12 pm 
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Hi,

I'd have to agree with Doos on this.

I'd also like to say that whoever wrote that definition (idiochromatic) should look for a new day job


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PostPosted: Thu Jul 26, 2007 6:12 pm 
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Doos,

You don't sound happy. :D
------------
Frank,

Would you like to apply for job at Random House?

How would you define "idiochromatic?" :?:


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PostPosted: Thu Jul 26, 2007 6:13 pm 
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Without over thinking it and simply answering the question, (the question didn't say based on those definitions) I'd say:

Peridot
Rhodochrosite

I guess one could argue a case for rhodolite, but, since it is a variety that is dependant upon a mix of 2 species even though the species may be idiochromatic, I'll dismiss it on a technical flaw.


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PostPosted: Thu Jul 26, 2007 6:31 pm 
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I'm going to agree with JB. Peridot and Rhodochrosite.


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PostPosted: Thu Jul 26, 2007 8:41 pm 
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I'm going to venture that rhodochrosite is the lone idiochromatic mineral in the list.

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PostPosted: Thu Jul 26, 2007 9:24 pm 
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I think I know what you are thinking ROM and considered that myself, but, that wasn't the question, was it? :)


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PostPosted: Thu Jul 26, 2007 11:29 pm 
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I learned that the word idiochromatic means that the color of the gemstone comes from its chemical makeup and not through an impurity.

Peridot is idiochromatic because iron is part of its makeup; no iron, no peridot.

Ruby is allochromatic because pure corundum (Al2O3) is colorless. It takes the impurity of chromium to color the corundum red.

With this understanding, I would say the following are idiochromatic:

Peridot ... rhodolite garnet ... tsavorite garnet ... rhodochrosite

The following are allochromatic:

Ruby ... amethyst quartz


Or, do I need to restudy?? 8)

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PostPosted: Fri Jul 27, 2007 1:01 am 
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I'm going with peridot and rhodochrosite.


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PostPosted: Fri Jul 27, 2007 1:07 am 
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Yes, I think I'm wrong. Peridot has Fe in its structure and I forgot about that.

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PostPosted: Fri Jul 27, 2007 9:13 am 
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Hi,

The gemmological defenition is a mineral that is coloured by elements that are an essential part of the chemical composition.
That is a not so fortunate definition unless you specifiy the rules.

If you translate it from greek, idio + chromatic just means self-coloured. So that applies to everything.

Rhodolite for instance has iron in its chemical composition. The colouring agent in rhodolite is said to be chromium, making it allochromatic. But if the iron would not be present, I'm sure that would affect the colour.

The same goes for tsavorite. Manganese is present in the chem. comp., but the colour is attributed to vanadium and chromium. Manganese itself is also a colouring agent and without it, the colour would also be different.

Food for thought.


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PostPosted: Fri Jul 27, 2007 9:37 am 
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See what you started, Bill 8) !

Okay, I'll give on the tsavorite, hesitantly, but according to GIA rhodolite garnet is colored by iron, part of its chemical composition, hence idiochromatic.

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PostPosted: Fri Jul 27, 2007 9:42 am 
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I'll add some fuel to the fire. This is one cool webpage:

http://realcolorwheel.com/crystal.htm

Hope you have a few minutes. 8)


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PostPosted: Fri Jul 27, 2007 9:48 am 
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It's way too early in the morning for that, JB :shock: .

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