We use cookies to show content based on your preferences. If you continue to browse you accept their use and installation. More information. >

FMF - Friends of Minerals Forum, discussion and message board
The place to share your mineralogical experiences

Spanish message board

Newest topics and users posts
07 Jul-09:40:41 Re: collection of firmo espinar (Firmo Espinar)
06 Jul-16:03:50 Re: collection of sante celiberti - a mineralogical trip through italy (Sante Celiberti)
06 Jul-14:02:46 Re: tourmaline? ural mountains? (Peter)
06 Jul-08:16:02 Re: tourmaline (Jordi Fabre)
06 Jul-07:30:08 Re: tourmaline (Bob Morgan)
06 Jul-01:05:33 Re: tourmaline (Peter Lemkin)
05 Jul-19:44:20 Re: tourmaline (Josele)
05 Jul-16:14:43 Re: tourmaline (Roger Warin)
05 Jul-16:12:10 Re: tourmaline (Bob Carnein)
05 Jul-16:00:27 Re: collection of sante celiberti - a mineralogical trip through italy (Sante Celiberti)
05 Jul-15:53:10 Re: tourmaline (Bob Morgan)
05 Jul-09:04:13 Re: tourmaline (Josele)
05 Jul-07:34:32 Re: tourmaline (Roger Warin)
05 Jul-06:45:51 Re: tourmaline (Mathias)
04 Jul-18:20:35 Popular minerals - elbaite from pederneira claim (Jordi Fabre)
04 Jul-16:53:00 Collection of bergur e. Sigurdarson (Bergur_e_sigurdarson)
04 Jul-16:06:30 Re: don lum collection (Don Lum)
04 Jul-15:24:10 Re: collection of sante celiberti - a mineralogical trip through italy (Sante Celiberti)
04 Jul-14:03:38 Re: collection of michael shaw (Michael Shaw)
03 Jul-15:27:11 Re: collection of sante celiberti - a mineralogical trip through italy (Sante Celiberti)
03 Jul-14:07:03 Popular minerals - chrysocolla coating quartz from the tentadora mine (Jordi Fabre)
03 Jul-09:01:07 Re: collection of firmo espinar (Firmo Espinar)
03 Jul-03:32:44 Re: a crystal collecting outing to ceres, south africa (Nakanvayul)
02 Jul-16:14:37 Re: tourmaline (Josele)
02 Jul-15:59:00 Re: collection of bergur e. Sigurdarson (Fiebre Verde)

For lists of newest topics and postings click here


View unanswered posts

Why and how to register

Index Index
 FAQFAQ RegisterRegister  Log inLog in
 {Forgotten your password?}Forgotten your password?  


The time now is Jul 07, 2020 10:54

Search for a textSearch for a text   

A general guide for using the Forum with some rules and tips
Rhodochrosite geodes
  Index -> Mines and Mineral Localities

View previous topic :: View next topic  
Author Message


Joined: 17 Apr 2008
Posts: 17
Location: Charlotte, North carolina

Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Feb 06, 2016 17:01    Post subject: Rhodochrosite geodes  

Sometime ago there was a brief thread discussing the rarity, or even existence, of Rhodochrosite crystals in true geodes (not just half-vugs). At the time John Cornish regaled us with his story about a red gemmy crystal in a quartz geode. Unhappily the proved to be hematite-included Calcite on analysis.

That they exist is confirmed by the presence in two famous Colorado collections but after 40 years of collecting, I had never seen even a photo of an example. Until now.

I have recently become aware of undeniable examples of such specimens in the collection of the National Mining hall of Fame and Museum in Leadville, Colorado. Photos of two of these are by Leonard Himes.

Unfortunately, there is no additional information about the locality. Legends of a "lost" locality are heard in Colorado. Now at least their existence is confirmed. Now the locality. It is said that these are from "Colorado" USA but no other information is available, even from the museum. Any further information would be appreciated.

Rhodo Geode 2 open.jpg
 Mineral: Rhodochrosite
 Dimensions: 6 cm
 Viewed:  10227 Time(s)

Rhodo Geode 2 open.jpg

Rhodo Geode 1.jpg
 Mineral: Rhodochrosite
Colorado, USA
 Dimensions: 7 cm
 Viewed:  10209 Time(s)

Rhodo Geode 1.jpg

Bill logan
Back to top
Reply to topic Reply with quote

Bob Harman

Joined: 06 Nov 2015
Posts: 697
Location: Indiana

Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 17, 2018 22:13    Post subject: Re: Rhodochrosite geodes  

This nearly 3 year old thread is of a topic that has interested me for some time. There were no responses so I will give a bit of explanation.

Referring specifically to midwest USA geodes of sedimentary origin, why are calcite (CaCO3) geodes so incredibly common while rhodochrosite (MnCO3) geodes, also a simple carbonate, virtually nonexistent? And this is also despite the fact that manganese rich calcite geodes do occur regularly in the geodes of a locality in Missouri (a picture of one of these is shown for comparison).

The answer seems to be in basic differences in formation of the sedimentary geodes themselves. Midwest geodes form either in invertebrate fossil voids existing in the mid Mississippian age hardening limestones or form as an anhydrite replacement in the hardening limestone.

Calcium carbonate is a basic component of the limestone, easily crystalizing into calcite at the low ambient temperatures of their formation. On the other hand, manganese, while found in the mid Mississippian limestones simply does not exist in quantities sufficient enough to collect into crystals known as rhodochrosite. That is what I am told. Only a few molecules are enough to make the manganese rich calcites, but not enough manganese carbonate molecules are present to make rhodochrosite crystals. Too bad for collectors!! Of course this does't address the original question of Colorado rhodochrosite in geodes.

Parenthetically, the original pictured examples from Colorado and not the Midwest, should have been properly cleaned before posting the photos. They would have looked more impressive.

 Mineral: Calcite (variety manganese-rich) on Quartz
Sheffler's Geode Mine, St. Francisville, Clark County, Missouri, USA
 Dimensions: large geode about 18 cm. The calcites are up to about 4.5 cm
mined in the 1980s. Acquired by me about 8 years ago.
 Viewed:  4929 Time(s)


Back to top
Reply to topic Reply with quote
Display posts from previous:   
   Index -> Mines and Mineral Localities   All times are GMT - 5 Hours
Page 1 of 1

Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum

All pictures, text, design © Forum FMF 2006-2020

Powered by FMF