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
24 Oct-11:17:10 Re: collection of michael shaw (Michael Shaw)
24 Oct-09:37:12 Re: collection of volkmar stingl (Volkmar Stingl)
24 Oct-09:28:16 Re: collection of michael shaw (Volkmar Stingl)
24 Oct-09:04:01 Re: collection of michael shaw (Michael Shaw)
24 Oct-03:54:43 Re: collection of tobi (Dany Mabillard)
24 Oct-03:50:24 Re: collection of tobi (Tobi)
23 Oct-23:28:11 Re: help found with american indian items (Philippe Durand)
23 Oct-15:08:16 Silvia's collection - classic portugese ferberite (Silvia)
23 Oct-13:59:45 Re: help found with american indian items (Lou B.)
23 Oct-13:56:06 Help found with american indian items (Lou B.)
23 Oct-13:45:52 Re: collection of tobi (Tobi)
23 Oct-12:29:41 Re: munich show (mineralientage) 2021 (Jordi Fabre)
23 Oct-12:23:20 Munich show (mineralientage) 2021 - like a new show (Jordi Fabre)
23 Oct-11:54:58 Re: collection of tobi (Tobi)
23 Oct-09:31:25 Re: munich show (mineralientage) 2021 (James Catmur)
23 Oct-04:07:52 Re: new generation for picture - ploum (Ploum)
23 Oct-01:16:33 Re: new generation for picture - ploum (Ploum)
22 Oct-23:13:53 Re: collection of volkmar stingl (Volkmar Stingl)
22 Oct-20:05:22 Re: new generation for picture - ploum (Silvia)
22 Oct-16:40:52 Re: don lum collection (Don Lum)
22 Oct-14:56:10 Re: don lum collection (Silvia)
22 Oct-14:10:58 Re: don lum collection (Don Lum)
22 Oct-13:40:23 Re: collection of sante celiberti (Sante Celiberti)
22 Oct-12:50:16 Re: new generation for picture - ploum (Ploum)
22 Oct-12:25:00 Re: collection of firmo espinar (Firmo Espinar)

For lists of newest topics and postings click here


RSS RSS

View unanswered posts

Why and how to register

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

Like
85947


The time now is Oct 24, 2021 11:19

Search for a textSearch for a text   

A general guide for using the Forum with some rules and tips
The information provided within this Forum about localities is only given to allow reference to them. Any visit to any of the localities requires you to obtain full permission and relevant information prior to your visit. FMF is strictly against any illicit activities related to collecting minerals.
What is this rock formation?
  
  Index -> What is it? - Where is it from?
Like
2


View previous topic :: View next topic  
Author Message

tfarris6124




Joined: 04 Jul 2021
Posts: 4

View user's profile

Send private message

PostPosted: Jul 04, 2021 19:42    Post subject: What is this rock formation?  

This is from central Texas on a high cliff over a small river. The bulbous form is strange sticking out on both sides of the flatter rock. The round part is about a six inch sphereish shape sticking out about two inches on either side of the flat. What makes the rock form like this? Is there something inside the round part? Thanks for your help.


Top Growth.jpg
 Description:
 Viewed:  1059 Time(s)

Top Growth.jpg


Back to top
Reply to topic Reply with quote
Like
1
   

tfarris6124




Joined: 04 Jul 2021
Posts: 4

View user's profile

Send private message

PostPosted: Jul 04, 2021 19:43    Post subject: Re: What is this rock formation?  

Other side view.


Bottom Growth.jpg
 Description:
 Viewed:  1070 Time(s)

Bottom Growth.jpg


Back to top
Reply to topic Reply with quote
Like
   

tfarris6124




Joined: 04 Jul 2021
Posts: 4

View user's profile

Send private message

PostPosted: Jul 04, 2021 19:44    Post subject: Re: What is this rock formation?  

Internal view.


Internal View.jpg
 Description:
 Viewed:  1052 Time(s)

Internal View.jpg


Back to top
Reply to topic Reply with quote
Like
   

Peter Megaw
Site Admin



Joined: 13 Jan 2007
Posts: 925
Location: Tucson, Arizona


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jul 04, 2021 20:35    Post subject: Re: What is this rock formation?  

What formation is it from? Edwards?

This looks like a textbook concretion...a banded onion-like body that forrms during diagenesis/lithification where something (fossil, organic nucleus etc) acts as a nucleus for deposition of successive layers of silica or carbonate or iron-oxides.Sometimes they're hollow...but not often in your neighborhood.

There are 4 questions

1. Is it chert (flint)? If it is you won't be able to scratch it with a knife or nail. If it's chert, do no more, enjoy it as a yard rock with a cool shape.
2. Is it carbonate? If so, it will scratch easily...and will most likely be fine graimed banded calcite unless it is from one of the strontium rich units in the area and may be celestine.
3. Is it solid? If it's hollow there may be crystals inside. If it is hollow enough you may be able to heft it and tell it's hollow. Find a rock you know is solid and about yhe same size and see if there's a difference. If it's solid leave it alone and enjoy your yard rock
4.if it feels hollow or if you're a gambler willing to exchange a cool complete yard rock for fragments...you can break or cut it open with a chisel or tile saw. If its from one of the Sr bearing units you might find celestine crystals. If not, most likely is calcite crystals...shiny if you're lucky.

I would give you low odds of a void being present...
I think you have a great yard rock with a built in mystery...
You can definitively solve the mystery anytime...

_________________
Siempre Adelante!
Back to top
Reply to topic Reply with quote
Like
1
   

tfarris6124




Joined: 04 Jul 2021
Posts: 4

View user's profile

Send private message

PostPosted: Jul 04, 2021 22:17    Post subject: Re: What is this rock formation?  

Wow thanks so much for the information.

I'm not sure of the formation it came from. Crews are cutting new roads in the area and digging up a lot of rock so I don't know for sure where it came from. I'm guessing Edwards, but maybe Comanche Peak? I don't know I'm in over my head here.

The flat rock surrounding the concretion is definitely chert. The concretion itself though seems to be different. I think I have scratched down past the outermost sediment and it still seems soft. It also has a sparkle to it that neither the sediment nor chert have making me think it might be calcite.
Back to top
Reply to topic Reply with quote
Like
   

SteveB




Joined: 12 Oct 2015
Posts: 191
Location: Canberra

View user's profile

Send private message

PostPosted: Jul 04, 2021 22:19    Post subject: Re: What is this rock formation?  

Looks like a limestone nodule. Should acid test the round rock as well as the surrounding matrix. Use a drop of hydrochloric acid or white vinegar and note any bubbles forming and how aggressively.. I’m more familiar with iron concretions (this isnt that) but might be other form of concretion.

Are you able to gather more from the location? Maybe find a broken round rock half to show its interior which will help.
Back to top
Reply to topic Reply with quote
Like
   
Display posts from previous:   
   Index -> What is it? - Where is it from?   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 2006-2021


Powered by FMF