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Green chert?
  
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Murray




Joined: 16 Apr 2017
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PostPosted: Dec 31, 2017 01:21    Post subject: Green chert?  

Hi folks.

I’m from the east coast of Queensland, Australia. According to the 1:250,000 geological maps this area is supposed to contain red, green and white chert, mudstone, acid tuff, limestone, and tuffaceous arenite.

I;m not familiar with green chert but given it's supposed to be in this area and this is the closest thing to green chert that I've found around here, It could be chert but it's more grey than green.

So is this likely to be chert?

Cheers,
Murray.



IMG_20171231_152438491.jpg
 Dimensions: 95mm x 70mm x 60mm
 Description:
 Viewed:  1771 Time(s)

IMG_20171231_152438491.jpg



IMG_20171231_152524038.jpg
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IMG_20171231_152524038.jpg


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SteveB




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PostPosted: Dec 31, 2017 01:55    Post subject: Re: Green chert?  

First check the sticky post on doing some basic tests like hardness and streak since its difficult to identify specimens from photo only.

Second I would call that colour grey, Green minerals tend to be very obviously green, unlike horse and dog colours. I would be leaning towards a chalcedony not a chert for that specimen, but not green. Are there agates in the location too? I used to get heaps from the Ipswich area in SE Qld.
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Anísio Cláudio




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PostPosted: Dec 31, 2017 19:28    Post subject: Re: Green chert?  

Hi,

Look this chert from Capitólio, Minas Gerais- Brasil.

Greetings,

Anísio Cláudio



silex verde.JPG
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Capitólio, Minas Gerais- Brazil
12 x 11 x 5 cm
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silex verde.JPG



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Coordinator of the mineralogical museum UNIFOR-University Center of Formiga, Minas Gerais, Brazil
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Bob Harman




Joined: 06 Nov 2015
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PostPosted: Dec 31, 2017 20:49    Post subject: Re: Green chert?  

Chalcedony and chert are similar, both being microcrystalline and cryptocrystalline quartz. Chalcedony is also fibrous microcrystalline quartz. However, most people do separate the two. Chert usually occurs as nodules in marl or marly limestone while chalcedony occurs as part of crystalline quartz or massive deposits. Flint is usually created from this massive chalcedony or even chert nodules and has been worked for tools and arrowheads by Native Americans for thousands of years. The chalcedony can occur in a wide variety of colors and shades, for example red colors might be jasper/carnelian while green shades might be chrysoprase, especially if nickel is found to be present.
Your example appears more consistent with being a piece of massive chalcedony of a greenish gray shade. BOB
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SteveB




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PostPosted: Jan 01, 2018 01:51    Post subject: Re: Green chert?  

That second example definitely looks like the original posters. Happy to be called wrong on this one, the pieces i can recall were an obvious green but small and some polished. I’m thinking a hand tool in my collection now might be chert, instead of flint i always called it (I received it as a child and flint tools i knew about at the time).
Looking more at the details of chert and chalcedony It’ll be hard to differentiate with home basic tests i feel :( Some more in situ clues could sort it i think to see its associations.
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Anísio Cláudio




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PostPosted: Jan 01, 2018 07:47    Post subject: Re: Green chert?  

Hi,

My sample is a metachert. It occurs associated with sandstones and quartzites of the Canastra Group. Corresponds to volcano-chemical facies / leaching. There are several colors. Green may be from finely disseminated pyrite.

Anísio

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Murray




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PostPosted: Jan 01, 2018 20:03    Post subject: Re: Green chert?  

Hi folks.

Steve - I'm just outside Gladstone. If there are agates here, I haven't seen any.

Anísio - that does look close. Mine may have fractured differently to your specimen. I'm not sure if that's significant.

We are in the Doonside Formation and are just to the east of the Boyne River Fault. Like most of the east coast, it's old volcanic. Red soil, lots of magnetite around, some quartz, some manganese, some red stone I thought was chert. I disagree with the 1:250,000 map in that I haven't seen limestone in this formation (yet). I may have seen some mudstone and it's not that common.

I have some llimestone from the Calliope Beds to the west and it is visible in one of the new images I'm posting. It is not from the Doonside Formation.

The first piece would have been hit by the slasher at some time, hence the damage. Rightly or wrongly, I damaged it some more in hopes of helping to identify it. See first image. It remains grey to my eyes.

I went for a stroll and picked up a few pieces of interest. The second image appears to me to have something very similar running through it. This is not an uncommon find around here.

The third image is of a couple of pieces I found yesterday and today. (The manganese is just there to remind me to clean it and the limestone is for a project I'm working on. They were not found today. The dendrite was from this morning.)

The last image is of a piece of chert/chalcedony where it was found. It is quite tricky to spot unless it has been damaged.

Please let me know if there is anything I can do to try and narrow this down further.

Cheers,
Murray.



IMG_20180102_100542803.jpg
 Mineral: Chert or Chalcedony
 Description:
Central Queensland
Various
 Viewed:  1528 Time(s)

IMG_20180102_100542803.jpg



IMG_20180102_100619259.jpg
 Mineral: Unknown mineral
 Description:
Central Queensland
60x50x35mm
 Viewed:  1528 Time(s)

IMG_20180102_100619259.jpg



IMG_20180102_100602268.jpg
 Mineral: Chert or Chalcedony
 Description:
Central Queensland
Various
 Viewed:  1540 Time(s)

IMG_20180102_100602268.jpg



IMG_20180102_095542153.jpg
 Mineral: Chert or chalcedony
 Description:
Central Queensland
15x25x35 mm
 Viewed:  1535 Time(s)

IMG_20180102_095542153.jpg


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