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alfredo
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Joined: 30 Jan 2008
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Posted: Jan 03, 2010 08:54 Post subject: Re: Seeking info on hyalite |
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Hyalite in the pegmatite cavities in Hirukawa, Japan, can get rather annoying - It encrusts lots of the older feldspars, micas and smoky quartz. Interestingly, it occurs in two generations, one of which fluoresces the typical green and the other fluorescing white! So uranium is not a universal activator in hyalite.
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parfaitelumiere
Joined: 02 Mar 2008
Posts: 153
Location: Auvergne
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Posted: Jan 03, 2010 09:21 Post subject: Re: Seeking info on hyalite |
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Hi,
There is a mistake with my photo,it seems it's lussatite after halite.
Some are talking of pseudo after melanophlogite.
The cubes are made of calcedony,but after halite or spomthing else,not Hyalite,I have mistaken on the photo.
on my photo it is calcedont and ct-opal-name of lussatite on mindat)
The hyalite is an amorphous glass containing water(an-opal)
Unlike most of opal species,it's not formed from aqua rich solution,it came from vapor deposit on cold surfaces.
The famous place where to find hyalit is Valec in tchek republic,and a place in mexico,don't remember the name,but we find some red topaz too.
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Hyalite on topaz 3,5cm mexico |
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14052 Time(s) |
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Hyalite 3,5cm Valec Tchek republic |
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14046 Time(s) |
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Peter Megaw
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Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Jan 03, 2010 10:29 Post subject: Re: Seeking info on hyalite |
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I suspect Pete Modreski is a better choice to answer the chemistry of this John, but I do have some experience in uranium exploration in volcanic piles, so I'll take a crack at the mechanics. The basis of our exploration program was to look first for volcanic piles that had lost uranium...by comparing the U content of glassy parts of the units (typically intra-caldera) with devitrified parts of the same units (typically outflows) and then looking for where the U might have been transported and trapped. We found lots of places that had lost U, but very little trapped U because there was nothing to trap it in the local environment where we looked. On an aside, we got pretty good at predicting which units had lost U simply by the presence and darkness of smoky quartz, which is caused by radiation damage. Quartz-eye rhyolites, either welded ash-flows or flow domes, typically had the highest original U content and the blackest quartz.
To return to the point: Rhyolitic (sensu latu) volcanics generally have elevated U with respect to more mafic compostions, and ash-flow tuff style volcanism tends to generate more glass than slower-moving styles that get a chance to crystallize. This means you have large volumes of relatively U-enriched glass shards that undergo devitirification during welding and degassing. Devitirification results in crystallization of abundant quartz and K-spar, but the U is incompatible and stays in the vapor phase until that hits some kind of depositional environment...geodes, cracks etc. and the U has nowhere else to go except be incorporated into the opal...or chalcedony.
Actually is does have somewhere else to go...into the local groundwater and on until it hits a reductive trap, like organic material. It also can get incorporated into calcite. In Mexico and other carbonate environments with overlying rhyolitic volcanic fields it is very common to see calcite veins that fluoresce yellow-green from U. These contrast nicely with the orange-red fluorescing Mn-bearing calcite veins deposited by the spent fluids left over from carbonate replacement deposit metals deposition. Very useful for separating structural environments in the field and in core! Practical mineralogy strikes again!
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Peter Megaw
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Joined: 13 Jan 2007
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Location: Tucson, Arizona
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Posted: Jan 03, 2010 10:48 Post subject: Re: Seeking info on hyalite |
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Many of the Mexican topaz rhyolites generate hyalite as a final coating phase. The pictured one comes from Mina Veronica in Zacatecas...Mike New of TopGem has produced these for years. Most of the time they burn off the hyalite with HF. There are fine filaments of a black mineral within the hyalite blobs...psuedobrookite? that do not survive the cleaning process either.
The Bohemian examples typically show well crystalized apatite (specific species unknown to me)...is this also vapor phase deposition?
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Matt_Zukowski
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Joined: 10 Apr 2009
Posts: 707
Location: Alaska
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Posted: Jan 03, 2010 20:17 Post subject: Re: Seeking info on hyalite |
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Bailey - I too want to encourage you to keep looking at minerals. There are so much cool things about minerals that you never stop being amazed by them. I have gotten my nieces to Tucson for two years and they totally love mineral specimens now. There are many mineral shows and clubs to attend. Go to: https://www.rockngem.com/showdates.asp (link normalized by FMF) for mineral shows and google up you local club if you are interested.. BTW, you must see fluorescent hyalite in person, in a dark room. Peter's pictures are good, but nothing beats seeing them yourself. Tucson always has a nice fluorescent display but I'll bet many other mineral shows do too.
No matter what you do - have fun and keep interested! Good luck!
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Peter Megaw
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Joined: 13 Jan 2007
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Location: Tucson, Arizona
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Posted: Jan 03, 2010 22:16 Post subject: Re: Seeking info on hyalite |
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Matt...how old are your nieces and are they coming this year...there's a gang of kids getting together at Tucson this year some competing (for $$$!!!) and some just enjoying the minerals. I am sure they'd be welcome and my daughter would be happy to communicate with them in advance about what's afoot
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Matt_Zukowski
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Posts: 707
Location: Alaska
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Posted: Jan 04, 2010 17:26 Post subject: Re: Seeking info on hyalite |
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One is 11 and one is in second grade. They aren't coming in this year until Sat, so they will only have one day at the main show. But if there is an age-appropriate kid thing to do on Sun, then please let me know and I'll get with their Mother.
Thanks.
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Peter Megaw
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Joined: 13 Jan 2007
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Location: Tucson, Arizona
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Posted: Jan 04, 2010 17:48 Post subject: Re: Seeking info on hyalite |
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The Main Show is appropriate for ALL ages...
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