Simple cooling after formation can generate a liquid inclusion that contains a bubble - at higher temperatures they will be a single phase (most gas-liquid inclusions that you see now in quartz were a single phase when they formed). And other things can happen - do you see the bubble in your bottle of lemonade before you open it? No, it is a function of a fall in confining pressure from above atmospheric to atmospheric (causing phase separation).
Sluicing at Reedy Creek Woolshed Falls
- Thread starter Bushy007
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Thanks!
Right, thanks for setting me straight there.
Of course the voids in quartz are not always negative crystals, it’s just that they are the most beautiful and therefore the most memorable,
Still, there’s a clear difference between the uniformly spherical bubbles in glasses and the shape of the voids in quartz.
You say "there’s a clear difference between the uniformly spherical bubbles in glasses and the shape of the voids in quartz". I have to disagree that this is a clear difference that can be in any way diagnostic. I have seen them uniformally spherical in some Victorian quartz from gold deposits (more commonly they are irregular and often elongated). Likewise, while they are never crystal shapes in glass, they are often elongated and irregular like this example in glass.
There are all sorts of reasons why bubble inclusions have a particular shape - for example some were simple fluid bubbles when the quartz formed, others subsequently modified their shape as the quartz cooled, others formed along fracture planes in the cooling quartz, others disaggregated after intitial formation of one big bubble, forming many tiny bubbles. And a person looking at an inclusion in a hand specimen will commonly see the almost-always present spherical shape of the vapour bubble in the liquid, rather than the outline of the liquid.
And of course quartz is much harder than glass, so the simple scratch test is far more diagnostic of whether a specimen is quartz or glass.
And as you say, negative crystal shapes when present can be quite spectacular!
I first saw the enhydros when a 14 year old prospector at Beechworth, And yes, they were not in crystals but had taken the shape of cavities - I think they were actually chalcedonic in the main.
Interesting. I always thought this was a reliable diagnostic feature. I’d be interstate in hearing about your experiences prospecting in Beechworth. Were you mainly looking for quartz etc or gold? Thanks for the beautiful negative crystal picture.
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Beechworth was initially when I was 14 - that is 60 years ago so not very relevant. I was looking for gold and gemstones (with some mild success). I still have my photos of "you will be shot" etc, signs on claims - there were extensive sluices in parts of Woolshed Creek - the Eldorado dredge was largely sunk at the time although you could still get onto it. You could get away with a lot as a 14 year old. Of course I have been back many times since. Most people think of Beechworth gold as from the town north to the falls then west down to Eldorado, but a lot of its gold actually came from upstream of that (south of the granite), and in drainages flowing westward like 3 mile creek. It produced nearly as much alluvial gold as e.g. Castlemaine. However it differed in that much of the alluvial was large tonnage-low grade (hydraulic sluicing, dredging), using a system of channels (races) cut from as far to the east as the Kiewa River.
Alfred Howitt the geologist (Howittville, Howitt St Ballarat, Mt Howitt, discoverer of Crooked River goldfield, led the search for Burke and Wills etc) walked there with his parents and they were among early prospectors there.
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