barrington tops geodes

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kawman

kawman

steve wardle
Joined
Jul 11, 2013
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Location
Taree, NSW
A few guys have been reading the same stuff as me saying that geodes up to 40kgs have been found years ago in riolites up along dog trap road 4 kms east of stratford out behind the coal mine at gloucester.. :| at long last I have met a person that was born there.. :) He says that he can get me onto the private propertys along the creek and back up into the ridges.. :p this is going to be epic for me after studying my local area for so long.. :) I will be looking for the riolites around that area and only then may the source of the geodes be found.. :) a good friend has seen a geode from about there some years ago.. the person would not tell him the exact spot it came from.... :/ one way or the other this will be proven to be crap (in geological journals) or be a great thing to find true.. :D
 
Go for it Kawman

I love the thrill of the hunt but will be happy to see a few trophy photos. :D
 
I cant wait to be introed to the local farmers and let loose on my 100cc bike.. it will make getting about the area a snap for an old bugger like me.. I am doing my best to be patient and not push the guys involved.. very hard to do when you are this close.. :)
 
I will add that riolites are a type of basalt.. It can take many differant forms...even volcanic dust.. find the riolites and the geodes should be there. I think that I will be looking for a basalt rock type that I will notice because it will be different to anything else I have seen localy.. :) 500,000 tons of riolites will be much easyer to find than looking for a 40 kg or less geode.. this should be fun.. :p
 
Sounds like you have some fun ahead, good luck with the hunt.

Rhyolite is not a type of basalt though. They are both fine grained, extrusive igneous rocks, but the mineral compositions are almost polar opposites with basalts being mafic and rhyolite felsic.
 
we are both right...it can be a rock called rhyolite bit like granite... but it is also a type of volcanic basalt... had me not sure of myself and googled it up.. At any rate I will be looking for something out of the local norm.. :)
shivan said:
Sounds like you have some fun ahead, good luck with the hunt.

Rhyolite is not a type of basalt though. They are both fine grained, extrusive igneous rocks, but the mineral compositions are almost polar opposites with basalts being mafic and rhyolite felsic.
Click to expand...
 
Lots of different ways to look at it I guess, I just like talking about rocks ;) .
Rhyolite is the felsic equivalent of basalt, so they both get extruded (lava flows) and cool very quickly, this means that the crystals do not have time to grow and the crystals in the groundmass can really only be seen under a microscope.
But chemically granite is similar to rhyolite and gabbro similar to basalt, but granite and gabbro are intrusive, so it forms underground where it cools more slowly and the crystals have time to grow big enough to be seen with the naked eye.

What blisters said was right on the mark. One of rhyolites main minerals is quartz which you will not find in a basalt (unless in a pocket that has been deposited after the basalt). Where as basalt has olivine, which you will not find in a rhyolite.
 
I went there a couple of years ago . The creek was filled with cows and even more cow crap , gave it a miss . Hope you get there after a good downpour to clean it up :)
 
I have been doing some research and I will be starting my search closer to the coal mine.. May even sneek over and have a look at their excavation for clues.. The paper says 4kms so 4kms it will be.. the 4kms mark is missed if you use the newer whenham cox road because it runs into the old dogtrap road 5.5 kms in from stratford..... I will also try to find a very old local and have a chat.. older people remember things that can be of use.. the creek starts at about 5.5 kms in and makes its way 14 kms up into the hills and is way off the 4kms paper says.. I will try to get out for a look next sat... I will look with an open mind because the geodes may already be liberated from their original beds and have been redeposited??? I know that the area is a basin with conglomerate in the bottom covered by a layer of coal and a thin crust of top soil under the mines.. :)
 
shivan said:
Lots of different ways to look at it I guess, I just like talking about rocks ;) .
Rhyolite is the felsic equivalent of basalt, so they both get extruded (lava flows) and cool very quickly, this means that the crystals do not have time to grow and the crystals in the groundmass can really only be seen under a microscope.
But chemically granite is similar to rhyolite and gabbro similar to basalt, but granite and gabbro are intrusive, so it forms underground where it cools more slowly and the crystals have time to grow big enough to be seen with the naked eye.

What blisters said was right on the mark. One of rhyolites main minerals is quartz which you will not find in a basalt (unless in a pocket that has been deposited after the basalt). Where as basalt has olivine, which you will not find in a rhyolite.
Click to expand...

Makes me wonder about the Labradorite from Springsure, which makes a nice faceted stone, if a little on the soft side. It can be found in it's crystalline form - square and rectangular pieces up to an inch long - in weathered basalt soil. I've also found it in bits of rock which I think are scoria. Scoria is extrusive like basalt? Must have cooled more slowly than usual to allow the formation of decent-sized crystals?

Sorry didn't mean to hijack this geode thread :)
 
Kawman it sounds like you have done your research, so I really hope you find what you are after. Keep an eye out though, you may also be able to find agatized rhyolite or even some nice obsidian.

Lefty, it sounds like the labradorite has grown as phenocrysts from fluid inclusions or maybe gas bubbles. These would have grown at a later stage, maybe because of another flow reheating the basalt or hydrothermal fluids I think.
 
I have read about geodes forming in other rocks besides basalt.. it was said that sometimes pockets can form when something in the rock breaks down or an ancient piece of wood ect rots away leaving a void that ground water builds crystals in .. sort of like agatised fossils ect.. I have an open mind and will have a good look about the area closer to the 4km mark mentioned in the book by lin Sutherland.. the book says agates and geodes up to 40 kgs can be found there.. This leads me to think that some digging has been done in the past and they may have left some signs behind.. I will not make it there this week because my prospecting buddy has secondary cancer in his back and will be getting radiation treatment.. poor bugger may not get over this.. one out of five chances they say...fingers crossed.. I will look into getting someone else that is interested to come out for a look about.. I am older myself and don't go out on my own in case something happens to me.. If this search comes up blank we will have a look up the creek into the ridges.. we will prove or disprove the myth for once and for all.. contacting lin Sutherland comes to mind... she /he has a webb site .... :)
 
I have noticed rounded white rocks in the roadway embankments along thunderbolts way in this area and a lot of white soft crumbly decomposed rock.. I have no idea about what is about the area that we will be checking out.. I have never stopped to look always doing 120kmh on my bike.. I will have a proper look at that as well... :)
 
checked out the two rock types you mentioned and the rocks on the roadside are more likely nothing of interest.. until I get there we don't know much at all.. the geology there is a basin with conglomerate covered with coal covered with a thin layer of top soil backing onto the rock that compose the ridges.. I don't know anthing else.. :)
 

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