![]() ![]() However, for a quick lab treatment process, the temperature needs to be higher (350-450 deg C) than attainable by sitting in the sun. Firstly, for this to happen requires the presence of Fe in its divalent rather than trivalent form (the trivalent form will change the amethyst to citrine). You are not the only person to report this. Your comment on amethyst changing to colourless if left in the sun for a few months is interesting. Either your local public library or uni library should be able to let you read a copy of both.for free. These books are not cheap and 'Gemstone Enhancement' is out of print with s/h copies trading at a premium price. The Fifteen Causes of Color' is the standard primer on the causes of colour and 'Gemstone Enhancement' is also very useful with specific regard to gem mineral species. If you want to get to grips with what goes on and which colour changes can be considered stable and which (in nature or synthetic) are unstable - and why - there are two books, both by Kurt Nassau (PhD), 'The Physics and Chemistry of Color. The turning of some amethyst into citrine by heating is one example. One way is to drive water out of a hydrated mineral - or it may otherwise alter the way that colour is produced in it. The molecular agitation cause by the heat can act in different ways. Heat is another way that nature (and man) use to change the colour of a substance. This fading (over even years) can be reversed in minutes by exposure to the shorter wavelengths of gamma radiation. A stone like kunzite will - inevitably - lose most of its colour slowly in sunlight. Sometimes colours are darkened or made more vivid by exposure to certain wavelengths and and sometimes they are faded. For a range of species, colour changes when exposed to radiation of UV and shorter wavelengths - or to particle bombardment. I say again this is true both of the geologically formed and the anthropogenic. The species beryl is a very good example of one which is naturally colourless and which can have any one of several colours, depending on the presence or absence of certain trace elements and, often, alteration to atoms in those chromophore elements by radiation or heat. Where a species is not idiochromatic (the colour is not intrinsic to the very nature of species) then such a species (called allochromatic) requires some exterenal influence to give it colour. This is a hard science topic and many of the treatments simply supplement what was begun naturaly - or which nature simply forgot to do. To really get to grips with your topic, requires a good understanding of the mechanisms by which colour is created (in nature or by man). ![]() Why do you suppose that kunzite has always been known as the Evening Stone? And do you imagine that the wonderful natural Utah topaz is light stable? > result of the failure of treatments, eg. > I suspect a lot of what you're seeing is the > Beryl is light sensitive? You're telling me that > unless you're talking about centuries-old stones. > Never heard that amethyst wasn't color-fast, These crystals will darken when exposed to sunlight for extended periods:īarite (Some barite can turn blue when exposed to sunlight)Īs always, I thank you! WILL be getting their place in my list of references along with a high recommendation :)ġ1th Jul 2013 02:30 UTC Owen Lewis Tim Jokela Jr Wrote: Turquoise only if coated with protective substance. Scapolite, Purple (if it is an irradiated specimen) Prasiolite (Green Quartz)- removed duh! on my part! :-( Thoughts? (on the list, not the best comment.LOL)īeryl (Aquamarine, Emerald, Goshenite, Heliodor, Morganite) I will re-research this. To be the best, you have to come to the best and ya'll are it :) Would that be ALL Apatite specimens? or more the fluoroapatite variety? I am currently doing research for my book and have been combing through many pages to make a list of crystals that fade or darken when exposed to sunlight. Recent Images in Discussionsĩth Jul 2013 16:20 UTC Kristi Hugs Good Morning :) Currier Digital LibraryOpen discussion area. ![]() Techniques for CollectorsOpen discussion area. Minerals and MuseumsOpen discussion area. Mineralogical ClassificationOpen discussion area. Lost and Stolen SpecimensOpen discussion area. ╳Discussions □ Home □ Search □ Latest Groups EducationOpen discussion area. ![]()
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