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GeneralHow many minerals show star asterism?
24th Nov 2014 05:09 UTCJames Pool
24th Nov 2014 08:11 UTCErik Vercammen Expert
24th Nov 2014 10:43 UTCSpencer Ivan Mather
Spencer.
24th Nov 2014 11:42 UTCAlfredo Petrov Manager
Rob Lavinsky has a kyanite (triclinic) cabochon with 6-rayed star, from Nepal.
24th Nov 2014 12:22 UTCSusan Robinson
24th Nov 2014 14:23 UTCLászló Horváth Manager
24th Nov 2014 15:49 UTCRob Woodside 🌟 Manager
24th Nov 2014 16:36 UTCHarald Schillhammer Expert
24th Nov 2014 17:09 UTCStephanie Martin
24th Nov 2014 17:45 UTCEverett Harrington Expert
thanks
E
24th Nov 2014 22:29 UTCOwen Melfyn Lewis
27th Nov 2014 17:33 UTCStretch Young
Regards,
Stretch
27th Nov 2014 18:39 UTCOwen Melfyn Lewis
Chatoyancy and asterism are two optical phenomena that can be occasionally observed in a slew of transparent/translucent minerals (and some glass look alikes). These words say nothing about the type of mineral or its crystal system. It's a pity that some speak of them as it they were types of gem. They are not. They are two related optical effects sometimes to be found in a range of gemstones. At best, the terms are descriptive of varieties of certain gemstones that are a distinguishing feature - as would be yellow sapphire, so is star sapphire. The cut of a gemstone can increase or suppress the show of these phenomena.
27th Nov 2014 18:41 UTCStretch Young
27th Nov 2014 18:43 UTCRob Woodside 🌟 Manager
27th Nov 2014 18:59 UTCStretch Young
My comments were not about calling a star or a cats eye a species. The gem world and the mineral world have two different list as to what qualifies as a species. Ruby, Emerald, Kunzite, Hiddenite, these are not species on the IMA approved mineral list. They are however names you will get on a cert from GIA. So when counting the number of species you have, it depends on whether you reference the mineral world or the gem world. The real problem is in talking about gems on a mineral site as these two worlds don't always mix well at least on a technical and/or academic level. And heated discussions often follow. Hence "my struggles" in talking about the number of species I have as I am an avid mineral collector as well. In the end I reference the gem world names since that is the majority of who is interested in them and who would cert and document them for insurance purposes.
Regards,
Stretch
27th Nov 2014 19:04 UTCOwen Melfyn Lewis
27th Nov 2014 19:21 UTCStretch Young
Regards,
Stretch
27th Nov 2014 19:34 UTCOwen Melfyn Lewis
-------------------------------------------------------
> Owen,
> My comments were not about calling
> a star or a cats eye a species.
Thanks for the clarification. I though you were.
>The gem world and
> the mineral world have two different list as to
> what qualifies as a species. Ruby, Emerald,
> Kunzite, Hiddenite, these are not species on the
> IMA approved mineral list. They are however names
> you will get on a cert from GIA.
Now there you do mis-understand. Those are the names of certain mineral *varieties*. They are not (as you say) the names of mineral species. There is no such thing as a gem species; there are only mineral species (Diamond), varieties of mineral species (Beryl var. Emerald), a few rocks (Lapis Lazuli) and a small range of organic materials (Amber, Coral etc).
>
> the number of species you have, it depends on
> whether you reference the mineral world or the gem
> world. The real problem is in talking about gems
> on a mineral site as these two worlds don't always
> mix well at least on a technical and/or academic
> level. And heated discussions often follow. Hence
> "my struggles" in talking about the number of
> species I have as I am an avid mineral collector
> as well. In the end I reference the gem world
> names since that is the majority of who is<
> interested in them and who would cert and document
> them for insurance purposes
For your gem collection, latch onto the idea of differentiating between a gem that is a bare-assed mineral species, Sillimanite, or a mineral variety Kunzite - or Spodumene var. Kunzite - as this may help make sense of things. It can be confusing when starting out. In the organisation of a large gem collection - or the organisation of an even larger number of photos of the same it's useful, many find, to index under mineral species (where applicable with sub-indices listing of the sundry mineral varieties. For myself, I also find it easier to keep organics, synthetics and simulants each in a separate collection, indexed by different rules.
27th Nov 2014 20:07 UTCHenry Barwood
27th Nov 2014 20:33 UTCRob Woodside 🌟 Manager
27th Nov 2014 21:17 UTCOwen Melfyn Lewis
-------------------------------------------------------
> The star opals reflect (no pun intended) the
> longer range order found in supramolecular
> crystallization. I've grown opals in the lab over
> the years and the domains will sometimes be of a
> regularity and size that would produce this
> phenomenon. The 3 and 6 ray stars represent
> trigonal and hexagonal domains, respectively. The
> catseye is simply the columnar domains on their
> side.
Henry, that's very interesting. So you think that in your opal, the encasing material is monocrystalline (quartz?) rather than hydrated silica? Do you get an isogyre pattern between crossed polars?
Do you grow common or precious opal (opal with play of colour)? If you have any images, I would love to see - show 'n tell even better - as I imagine would others. Gilson sold out his synthesisation knowhow to Kyocera, Japan who, AIUI, have tweaked his work and filed for a Japanese patent (the same for Gilson lapis).
I happened to have the good fortune to examine (basically) a small collection of Gilson's synthetic precious opal only last week. At it's best, it is dangerously close to fine quality natural. Strangely, based on the dates of the examples I saw, the earlier stuff was better than what he was turning out
out a decade later, just before he sold out. Economics or rushing to produce volume - who knows.
27th Nov 2014 22:18 UTCHenry Barwood
There are a lot of methods of producing opal out there, some commercialized and some just small lab techniques. I quit fooling with it 12 years ago when I left the refractories industry for academia. Guess I need to pull out my research files sometime. I remember hardening them with several methods, but there was no incentive to try and carry it any farther.
I used to keep bottles of the settled opal arrays in my office for visitors to look at. Got a lot of comments, but inevitably someone would pick them up and the agitation would destroy them. Of course they came back, but it took a few weeks to re-form!
27th Nov 2014 23:56 UTCOwen Melfyn Lewis
Should you have the time and interest to dig out your old notes, these would be wonderful to learn from.
28th Nov 2014 00:16 UTCHenry Barwood
28th Nov 2014 00:49 UTCGreg Dainty
28th Nov 2014 01:20 UTCStretch Young
You can take a a green spodumene crystal with a chrome chromophore from Hiddenite, North Carolina and when you look it up on mindat it will be spodumene variety hiddenite. You then put that same crystal in your competition case at a show and you label it the same according to mindat and you will gets points taken off because varietal names are not valid according to the IMA which is what the AFMS follows for valid species lists. You then facet that crystal into a gemstone and you send it off to a gem lab and because of the chrome chromophore it will come back as hiddenite and have a much higher value than if you you sent in a green spodumene that had no chrome chromophore.
Since IMA does not recognize hiddenite and and gem labs do and the fact that the gem labs make a distinction between hiddenite and green spodumene and assign different values to the two, the fact of reality is the two industries have two different list of species. With Mindat you can even argue that a third list exists.
Other examples are pink sapphire, emerald, pariaba tourmaline and I have even seen cert's on "bixbite (natural red beryl)", their words not mine.
Mindat is different in that they do track varieties (and all the local/nicknames) which is a big help in trying to unravel what is what and serves a huge role in education. Something the IMA does not do and something the gem world only does for thousands of dollars.
In my opinion the IMA and the gem lab world need to get married and maintain a unified list and then educate the public. Mindat would be a good place for them to start.
The following link is the official IMA list, you will not find kunzite, emerald, sapphire etc on this list (you will find them on gemstone cert's without being listed as a variety).
http://pubsites.uws.edu.au/ima-cnmnc/IMA_Master_List_%282014-09%29.pdf
This only proves my original point, "The argument on mineral names vs gem names has been a real struggle, but in the end, you send a stone into GIA (or any gem lab) and they call it by it's gem name not its mineral name." Although I agree that a majority of the time those names are one in the same, the mineral name. The fact is that gem labs don't look up their names on mindat or the IMA lists, they have their own lists which even vary between gem labs. I know of gem dealers that will send their stone to different labs and keep the one cert they agree with and throw the others away. Or even use one cert in one country and another cert in a different country (pink sapphire vs ruby).
Like it or not that is the real world and that is the one I understand.
Regards,
Stretch
28th Nov 2014 02:21 UTCOwen Melfyn Lewis
-------------------------------------------------------
> Since IMA does not recognize hiddenite and and gem
> labs do and the fact that the gem labs make a
> distinction between hiddenite and green spodumene
> and assign different values to the two, the fact
> of reality is the two industries have two
> different list of species.
No.I think you are still confused. There is only one list of mineral species. As a generality, gemology uses that list. Tourmaline is one exception to that rule, where, for good reasons, gemmology opts to use the group name and not (except for very narrow academic purposes) the species names. Gemmology also used varietal names for as, you know, different varieties have remarkably different market values.
Rather like American English and Standard English, (or Latin-American Spanish and Iberian Spanish, there is a standard and common vocabulary shared by the two -ologies. However, if one deals with both -olgies, it is important to know the differences in vocabulary and allow for them in one's dealings.
.
> In my opinion the IMA and the gem lab world need
> to get married and maintain a unified list and
> then educate the public. Mindat would be a good
> place for them to start.
That might be nice but it will not happen because there is only partial overlap in the focus of their interests - and the gap is widening rather than closing. So what? Difference is neither better or worse - it simply reflects differing aims. Understanding and tolerance and an ability to use both forms of the language is what is (IMHO) required. Neither party has a monopoly of useful truths.
> This only proves my original point, "The argument
> on mineral names vs gem names has been a real
> struggle, but in the end, you send a stone into
> GIA (or any gem lab) and they call it by it's gem
> name not its mineral name." Although I agree that
> a majority of the time those names are one in the
> same, the mineral name. The fact is that gem labs
> don't look up their names on mindat or the IMA
> lists, they have their own lists which even vary
> between gem labs. I know of gem dealers that will
> send their stone to different labs and keep the
> one cert they agree with and throw the others
> away. Or even use one cert in one country and
> another cert in a different country (pink sapphire
> vs ruby).
As science evolves, so does language. Language in human rather than academic usage can take a long time to follow the revelations of science. Of course a 'pink sapphire' should logically be termed a (weak) ruby but most of the trade (jewellery) has not found a way of relating this change of status to the marked different in prices attainable for the two. So what? It'll come. Time once was, before science showed why it should not be so, that peridot (not forsterite, please) and bright green tourmaline were sold as emerald :-) Not to mention red spinel as ruby etc....
As any dealer will tell you, half the time whether a stone is a ruby or a pink sapphire depends of whether in negotiation one is the buyer or the seller :-) Again, so what? For one's collection, index under corundum and, according to taste, sub-index as ruby or pink sapphire. 'I say tomato and you say tomaeto'.... Best call the whole thing off :-)
Best,
Owen
28th Nov 2014 12:55 UTCRay Ladbury
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