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Keokuk.
  
  Index -> What is it? - Where is it from?
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vic rzonca




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PostPosted: Nov 19, 2019 09:08    Post subject: Keokuk.  

This question is for Bob Harman. Didn't he write the book on Keokuk? Regardless, I would like an identification for the white, powdery filling in this Keokuk geode. The specimen is about 20 cm. in diameter. I received it in an old collection, with no ID, but I'm sure it's a Keokuk, it was with several dozens of others and the collector was a regular visitor to the area. All guesses welcome.Thanks.


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Kevin Conroy




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PostPosted: Nov 19, 2019 09:53    Post subject: Re: Keokuk.  

Hi Vic, I don't want to steal Bob's thunder as to the identification of the white stuff so I'll avoid answering that. I do want to pass on that geodes like this are found in several locations in Iowa, Illinois and Missouri where the Warsaw Formation outcrops. Please see: https://www.mindat.org/photo-540814.html
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vic rzonca




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PostPosted: Nov 19, 2019 10:10    Post subject: Re: Keokuk.  

Thanks Kevin. I use, probably wrongly, Keokuk as a generic term for the material from that area. My collection went from no Warsaw Formation geodes to dozens in one step. I would suppose the specimens from one locale are unique to that site and identifiable from other sites. I would file this, for me, as an unknown known. So much to know, so little brain power.
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Bob Harman




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PostPosted: Nov 19, 2019 10:21    Post subject: Re: Keokuk.  

Vic,
The definitive work on Keokuk geodes was the 1969 Stephen Sinotte book "The Fabulous Keokuk Geodes Vol I". A follow up pamphlet also was written, but to my knowledge, no Vol II ever appeared. Sinotte lost interest after his collection was damaged during a messy divorce. Sinotte then worked for Upjohn Drug, now part of Pfizer Drug in Michigan.

The Kevin C picture of the Keokuk geode beds was uploaded several years ago to Mindat. The example that you show, based on its large size, quartz crystals and rind , is most likely from Clark County Missouri.
There is the small eccentric quartz crystal lined cavity with the adjacent whitish area of interest, not within the cavity. Most unusual. It should either be the clay mineral kaolinite or a sedimentary type carbonate mineral so try some vinegar or dilute HCl to see if it fizzes. Otherwise, I favor something like kaolinite. Bob
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Bob Harman




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PostPosted: Nov 19, 2019 11:33    Post subject: Re: Keokuk.  

This seems an appropriate time and place to give a primer on Midwest sedimentary type geodes.

These rock structures occur where certain layers of mid Mississippian age limestone approach the surface. The localities include one site in Michigan, the Wallace Stone Quarry, near Bayport. One locality near Wymore in SE Nebraska, several localities near Woodbury Tennessee and multiple localities thru central Kentucky, South central Indiana and the Keokuk beds of SE Iowa, West central Illinois and adjacent NE Missouri.

The Keokuk beds are the most famous because the chambers of commerce in this area has marketed geodes and geode collecting as a tourist attraction. There is a yearly festival with several family friendly fee for collecting sites in the area. Indiana examples are under appreciated as they have not been adequately publicized; many collectors consider highest quality Indiana examples to be the best of all.

The geodes are a rock structure composed of 1 or several minerals. Like all minerals, millions of low end and ordinary examples are found, but the higher the quality of the finds, the more rare the examples become.
So like all minerals, very hi end geodes command hi prices. In fact very hi end examples are much more difficult to find in the mineral market place than some hi end mineral species.

Some collectors "pooh pooh" geodes, but occasional hi end Midwest geodes, and geodes of other types, routinely have their quality areas culled out to make them into more traditional mineral specimens. This is similar to areas of Brazilian amethyst/calcite being culled out, or barite/calcite being culled out of South Dakota concretions or celestine crystals being culled out of Madagascar geodes. All become quality traditional type mineral specimens.

Geode collecting in the US Midwest has been a family affair for many many years. Millions of geodes, not only were collected, but many collected examples, both by adults and youngsters were discarded as youngsters grew up or their interests changed. This is why so many geodes are found where they did not originate from.

The real importance of Midwest geodes is that, for many youngsters, it was their entrance into the world of serious mineral collecting, geology, and the geological sciences.
Bob
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Jared




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PostPosted: Nov 19, 2019 11:46    Post subject: Re: Keokuk.  

Here is a guidebook for a field trip I ran last year for the clay minerals society. The locals were dumbfounded by large group of mostly foreigners excitement over the "white stuff"! Keokuk geode kaolinite is used as a standard for x-ray diffraction.


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Kevin Conroy




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PostPosted: Nov 19, 2019 13:33    Post subject: Re: Keokuk.  

Jared, you nailed it. By the way, have you ever noticed a correlation between the presence of the kaolinite and some of the accesory minerals (especially sphalerite and barite)? As a collector I was always happy to find a location with kaolinite, because I almost always also found minerals besides quartz and calcite in the geodes.

Vic, there are a few locations that produced unique looking geodes, or distinct looking crystals in them, but the vast majority look so similar that it's almost impossible to tell for sure if a geode came from a certain location. The most notable exception to this are the geodes found near Niota, Illinois that contain rich amounts of natural bitumen. Very few folks want even one of these in their collection because they are EXTREMELY messy!
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Bob Harman




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PostPosted: Nov 19, 2019 13:44    Post subject: Re: Keokuk.  

I think Kevin that you will see that I favored Kaolinite before Jared posted, altho his paper did help nail the id.

In addition several sites host unique geodes, both in the Keokuk beds and the Indiana/Kentucky beds. In Indiana the geodes of the In 56 road cut in Washington County are quite unique as the host dolostone allows brightly colored dolomite to stand out like nowhere else. Bob
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PostPosted: Nov 19, 2019 13:52    Post subject: Re: Keokuk.  

Worth noting on the subject of Keokuks is that the Matilda and Karl Pfeiffer Museum in Piggott, Arkansas has a superb collection of Keokuks she bought from Steve Sinotte. Many are posted on line, but this is a really cool well off the beaten track museum only an hour or so from Nashville. It sits next door to the Pfeiffer-Hemingway house where Ernest wrote a Farewell to Arms...he was married to Karl's sister.

They have exhibited a spectacular example with a huge wurtzite crystal at Tucson a number of times...

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vic rzonca




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PostPosted: Nov 19, 2019 17:05    Post subject: Re: Keokuk.  

Kevin, et al., would the kaolinite host the rarer minerals or is it more an indicator for the possible presence of them in the deposit? I have an impulse to probe the kaolinite. Yes -no?
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Jared




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PostPosted: Nov 19, 2019 17:18    Post subject: Re: Keokuk.  

Kevin Conroy wrote:
Jared, you nailed it. By the way, have you ever noticed a correlation between the presence of the kaolinite and some of the accesory minerals (especially sphalerite and barite)? As a collector I was always happy to find a location with kaolinite, because I almost always also found minerals besides quartz and calcite in the geodes.

Vic, there are a few locations that produced unique looking geodes, or distinct looking crystals in them, but the vast majority look so similar that it's almost impossible to tell for sure if a geode came from a certain location. The most notable exception to this are the geodes found near Niota, Illinois that contain rich amounts of natural bitumen. Very few folks want even one of these in their collection because they are EXTREMELY messy!


Hi Kevin. No, I have never observed a correlation with kaolinite and accessories (i.e. sphalerite). I've observed kaolinite in geodes containing solely quartz, as well as with most the other typical accessories (barite, calcite, dolomite, marcasite, and sphalerite).

With regard to the bitumen geodes, I'm considering running a field trip next fall for AAPG to look for these hydrocarbon geodes. To each their own!
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Bob Harman




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PostPosted: Nov 19, 2019 17:53    Post subject: Re: Keokuk.  

Vic, If your example was a solid geode with calcite, I would, by all means, say etch it out to find pristine secondary minerals protected within the enclosing calcite.
With kaolinite, I have no experience, but feel doing nothing is the best way to go. Bob
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Kevin Conroy




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PostPosted: Nov 19, 2019 20:23    Post subject: Re: Keokuk.  

I agree with Bob. You have a very aesthetic kaolinite geode, and I would keep it as is.
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vic rzonca




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PostPosted: Nov 20, 2019 07:04    Post subject: Re: Keokuk.  

Advice taken. It's always easier to do nothing. Done. Thanks folks.
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Jared




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PostPosted: Nov 26, 2019 11:07    Post subject: Re: Keokuk.  

For fun, and motivated by Vic's post, I took a quick look at some of the kaolinite under my new SEM. It was difficult to get quick high resolution photos on loose crystals without properly mounting and coating but I was still able to capture the high crystallinity of the kaolin.

Clay are mineral too :)



20191119_162359.jpg
 Mineral: Kaolinite
 Locality:
Jacob's Geode Mine, Hamilton, Hancock County, Illinois, USA
 Dimensions: 6 cm
 Description:
 Viewed:  340 Time(s)

20191119_162359.jpg



kaolinite_001.jpg
 Mineral: Kaolinite
 Locality:
Jacob's Geode Mine, Hamilton, Hancock County, Illinois, USA
 Dimensions: .1 mm
 Description:
 Viewed:  342 Time(s)

kaolinite_001.jpg



kaolinite_005.jpg
 Mineral: Kaolinite
 Locality:
Jacob's Geode Mine, Hamilton, Hancock County, Illinois, USA
 Dimensions: .03 mm
 Description:
 Viewed:  341 Time(s)

kaolinite_005.jpg


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Bob Harman




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PostPosted: Nov 26, 2019 12:25    Post subject: Re: Keokuk.  

Jared, Interesting Jacob's Geode Mine example.

Here are 2 Keokuk geode beds examples, collated together to show how hi end collectible examples look. Bob



fullsizeoutput_2bc2.jpeg
 Mineral: Manganese rich Calcite on Quartz (variet smoky)
 Locality:
Sheffler's Rock Shop and Geode Mine, Alexandria, Clark County, Missouri, USA
 Dimensions: See the ruler
 Description:
A very large well displayed and photogenic example
 Viewed:  317 Time(s)

fullsizeoutput_2bc2.jpeg



fullsizeoutput_24cf.jpeg
 Mineral: Calcite
 Locality:
Iowa, USA
 Dimensions: Specimen 6 cm. Calcite 3 cm
 Description:
pink calcite on iridescent pseudocubic brown calcite
locality: Iowa portion of the Keokuk geode beds
A double terminated pink "pagoda" calcite
 Viewed:  316 Time(s)

fullsizeoutput_24cf.jpeg


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