Talk:Opal

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Talk page contains some serious questions about facts in the article. These may have been corrected (or not), but inline citations would assist greatly in verifaction.

Expansion of sections needed also.
Subspecies currently grouped under this article. Breakout as article length dictates.
Opal Grading not covered sufficiently.
Opal and mythology behind/origin bad luck

SauliH 17:22, 30 January 2007 (UTC)

Subspecies that should find mention:

SauliH 17:27, 30 January 2007 (UTC)
This article is supported by WikiProject Gemology and Jewelry, gemstones subpage.
WikiProject Gemology and Jewelry To-do:

Contents

[edit] Value of opals

Opal is the [Queen of Gems]. No gemstone can match its spectacular 'play of color' or uniqueness. Australia produces 95% of the world's opal. Australian opal is sedimentry, whereas other opal from countries such as Indonesia, America, Peru, Mexico, Hungary and Poland is mostly volcanic.

Quality opal commands a lower price per carrot than diamond and is magnificent.

  • If you are familiar with the Rappaport Diamond Price Report, you will find that your statement is false regarding price per 'carrot', I think you mean carat, don't you? We can agree that high-quality gem grade opal is magnificent, but diamonds are graded on an established scale of quality while the valuation of opal is much more haphazard.T.E. Goodwin 07:48, 1 December 2006 (UTC)

[edit] Formation

There should be something on how opal forms

  • I concur. The geogenesis of opal is very interesting but complex to describe. As a Graduate Gemologist, I deal with opals on a daily basis and have been studying them for over 27 years. I will try to add some information on the fly here when I can find some time to go through my past lecture notesT.E. Goodwin 07:55, 1 December 2006 (UTC)

I hope that something is mentioned of the work of Len Cram, an Australian opal expert who has apparently been able to grow "natural" opals (simulating the way they were created in nature) in his home with a mixture of electrolyte, silica, water, alumina and feldspar. This technique produces opals indistinguishable from natural opals, unlike the synthetic ones currently mentioned in this article, and it overturns previous theories of opal formation involving sedimentary depositing of silica gel over millions of years. I am just a layman on this topic but that is what I have read. Lomacar 22:50, 1 December 2006 (UTC)

A Nov 27, 2007 Physics World article (http://physicsworld.com/cws/article/news/31941) by Hamish Johnston provides some information about the formation, composition and new methods of finding opal based on new research that shows that uranium is present in opal. More information is available in The Australian Gemmologist (2007) 23, 160-176, available online at http://www.australiangemmologist.com.au/images/1207opalarticle.pdf

Geologist Brian Senior and physicist Lewis Chadderton have determined that the optical properties of opal stem from the inclusion of tiny quantities of uranium during formation of the stone. Precious opal's play of color is caused by diffraction of light in a regular superlattice of 200 nm silica spheres. The superlattice forms as a result of the presence of the uranium and its decay products which act as seeds for the silica spheres during sedimentation.

The researchers have developed a method of opal hunting based on detection of gamma ray emissions from the decay of uranium contained in the opal. By drilling 3 holes and taking gamma ray measurements at small intervals the team has been able to triangulate the approximate location of opal deposits. The article from The Australian Gemmologist provides great detail of this method and results of field tests.(anon 9:25 CST Dec 14 2007) —Preceding unsigned comment added by 65.174.156.30 (talk) 15:39, 14 December 2007 (UTC)

[edit] article problem

See this slashdot comment:

How do tech-savvy people use it? Not at all. (Score:1) by MsWillow (17812) * Alter Relationship on Friday October 07, @01:12PM (#13736584) (Last Journal: Monday October 03, @03:42AM)

The few times I've checked it against other, reliable sources, it's failed miserably. I'm an avid lapidary. One gemstone near and dear to my heart is precious opal. I checked Wikipedia here [wikipedia.org] for what causes "play of color." They're claiming it's an interference pattern caused by parallel plates formed inside the stone. That's wrong.

Opal is amorphous. It fractures with a conchoidal shape. There are no microscopic parallel plates in opal, tho there are in labradorite. Opal's color play is caused by a regular pattern of silica microspheres, all the same size, forming a diffraction grating.

Opal's colors are pure like a rainbow. You'll never see metallic bronze, or metallic gold, coming from an opal, because of this, but you will see them coming from labradorite.

Their explanation was shown false some 25 years ago, with scanning electron microscope photos of precious opal. Why are they propagating a factual falsehood? And, more importantly, if they do this on a subject that I know well, what happens on subjects where I know little? How can I trust them???

[edit] additional article problem

The article claims that 'opalescence' is often used erroneously to refer to what is more accurately termed 'play of color', but Merriam-Webster defines the adj. opalescent as 'reflecting an irridescent light', and irridescence is defined as 'a lustrous rainbowlike play of color caused by differential refraction of light waves.' Maybe there is a conflict between technical and common definitions, but if MW supports the use of 'opalescence' to refer to 'play of color' in common speech, I believe it. Can someone address this? It sounded like whoever wrote that in the article knew what they were talking about, so I'm hesitant to change it without consultation. cmac 03:27, 30 December 2005 (UTC)

Rather than "play of color," wouldn't the correct term be pleochroism? user:mapetite526
  • "Play of color" is the commonly recognized gemological term. Because opal is singly-refractive isotropic, rather than doubly-refractive anisotropic, it cannot display pleochroism.T.E. Goodwin 07:32, 1 December 2006 (UTC)

[edit] Superstition

I've heard that opal is bad luck to own unless it's your birthstone. Can anyone confirm that this is a more widely-known belief? --Clay Collier 05:28, 23 October 2006 (UTC)

I've heard this too, I don't believe it though. I own an opal ring but am August born. But yes, someone mentioned this to my Mother once I think. --GracieLizzie 12:27, 17 November 2006 (UTC)
  • According to "Gems" 4th Edition by R. Webster, pg. 230 ,"From Roman times until the early seventeenth century it was held in high esteem, but during the eighteenth and nineteenth centuries it fell into disfavour in the belief that the stone was a bearer of ill-fortune, a belief which was probably based on a Teutonic superstition. Others say that this disfavour came from the influence of Sir Walter Scott's novel 'Anne of Geierstein' in which opal played such a malignant part. It seems more probable, however, that Scott concieved the idea of an opal of evil influence from an already exisitng belief."

T.E. Goodwin 07:11, 1 December 2006 (UTC)

[edit] Merge

The result of Wikipedia:Articles for deletion/Boulder opal was that Boulder opal should be merged into this article and redirected. If someone more familiar with the topic could merge the relevant details and then redirect Boulder opal to Opal, that would be great. Thanks! ···日本穣? · Talk to Nihonjoe 23:33, 3 January 2007 (UTC)

Hasty decision! An article only weeks old gets slated for deletion... Boulder opal is very distinct from solid opal and should eventually have it's own article. SauliH 07:43, 22 January 2007 (UTC)
Boulder opal is indeed a different "animal" and certainly deserves it's own article, SauliHT.E. Goodwin 23:20, 30 September 2007 (UTC)
Merged a little, most redundant or not really useable. Made redir. Seems boulder opal is simply opal as either fracture fillings or concretions in a dark ironstone - can't really see that it needs a separate article, don't need to promote it for the Aussies. Gem variety articles are mostly spam attractors. Vsmith 12:02, 22 January 2007 (UTC)

[edit] What are the limits of coverage of this article?

I see that this page is "supported" if that is the right term by the Gemology & Jewelry project. Therefore, I am not sure whether that would limit adding short sections on the following:

(i) what is known about the "structure" of opal/opaline silica; e.g. opal-C opal-CT, opal-AG etc.. which have slightly different structures on a more local scale. This might not interest gemologists so much as mineralogists/crystallographers, but it would seem to be quite useful to have a resume on here.

(ii) opal is classed as a natural photonic crystal. The page on this topic links to this page and has a picture which was probably originally uploaded for this page. Do a search on Google and see how many links come up under opal & photonic crystal. There is rightly a completely separate page on this topic, but I think it would be good to put a link to photonic crystals somewhere on this page, at the very least under "See Also", since a lot of other people looking up opal might be coming from this field. Opal is almost iconic in this field.

(iii) Organic occurrences of opal/opaline silica: in leaves, some animals etc.

I think these topics should be covered somewhere, but I don't want the anger of the world's gemologists on my head. I'd like to hear some comments on whether people would like short sections at the end of this article or to think about a separate page. Personally, my preference would be to add such sections to this article, since that would fit what I think should be done in an encyclopedia. Judge Nutmeg 15:22, 2 March 2007 (UTC)

Since there were no howls of outrage to my suggestion, I added a contribution on local structure of opal Judge Nutmeg 15:42, 14 March 2007 (UTC)

Technical Problem: The Andamooka Opal reference, which refers to Queen Elizabeth II, links to the RMS Queen Elizabeth II (the ship) when it should, I assume, go to the monarch. Unless someone presented the Andamooka to the RMS QEII.

[edit] 30 April 2008 Edits

I couldn't quite figure out how to undo some vandalism so I just saved an earlier version of the article. It looks good now. Sorry that I didn't post edit summaries. Makeemlighter (talk) 04:02, 30 April 2008 (UTC)