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
28 Mar-09:37:50 Re: 2 unknowns co-occurring with caledonite, grand reef mine, az (Cfrench58)
27 Mar-19:47:08 Re: 2 unknowns co-occurring with caledonite, grand reef mine, az (Pete Richards)
27 Mar-16:15:44 Re: 2 unknowns co-occurring with caledonite, grand reef mine, az (Cfrench58)
27 Mar-15:18:59 Re: 2 unknowns co-occurring with caledonite, grand reef mine, az (Alfredo)
27 Mar-14:39:29 2 unknowns co-occurring with caledonite, grand reef mine, az (Cfrench58)
27 Mar-05:21:48 Re: the mim museum in beirut, lebanon (Mim Museum)
27 Mar-05:03:26 Re: trying to find information on rose/pink quartz and tourmaline associations. (Ning)
27 Mar-02:39:50 Re: the mim museum in beirut, lebanon (Tobi)
27 Mar-00:23:28 Re: collection of volkmar stingl (Volkmar Stingl)
26 Mar-00:53:41 Re: collection of volkmar stingl (Volkmar Stingl)
25 Mar-13:32:10 Re: collection of michael shaw (Michael Shaw)
25 Mar-00:25:58 The mizunaka collection - quartz (Am Mizunaka)
23 Mar-13:35:22 Re: collection of firmo espinar (Firmo Espinar)
22 Mar-08:32:28 Re: collection of michael shaw (Michael Shaw)
22 Mar-04:20:41 Re: the mim museum in beirut, lebanon (Mim Museum)
21 Mar-22:49:19 Re: green seam. Looks like it in a state of decay. (Ning)
21 Mar-22:47:40 Re: green seam. Looks like it in a state of decay. (Ning)
21 Mar-22:45:25 Re: green seam. Looks like it in a state of decay. (Ning)
21 Mar-15:34:23 Re: the mizunaka collection - quartz (Am Mizunaka)
21 Mar-14:35:08 Re: jim’s mineral collection (Jim Wilkinson)
21 Mar-14:15:36 The 4th phoenix heritage mineral show (phms) hosted by mineralogical society of arizona (m (Chris Whitney-smith)
21 Mar-04:36:10 Re: the mizunaka collection (Tobi)
21 Mar-04:11:47 Re: jim’s mineral collection (James Catmur)
20 Mar-23:34:15 The mizunaka collection - quartz (Am Mizunaka)
20 Mar-18:13:16 Re: jim’s mineral collection (Jim Wilkinson)

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
111802


The time now is Mar 28, 2024 11:55

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.
Black thin layer help id
  
  Index -> What is it? - Where is it from?
Like


View previous topic :: View next topic  
Author Message

Robson Vieira




Joined: 05 Jan 2017
Posts: 28
Location: São Paulo

View user's profile

Send private message

PostPosted: Dec 23, 2019 10:33    Post subject: Black thin layer help id  

Hi everyone. I have found a little piece of basalt and it has a thin layer of a shiny black which I would like to know what it is. Follow the features of the LAYER only
Color: dark brown to black
Luster: submetallic
Streak: ochre to black
Hardness: 3 to 3,5 scratched by a fluorite chunk
Cleavage: none
The stuff is brittle a little bit.
Would it be just a chemical or organic deposition material?

The piece was found in a basaltic region.

Thanks



20191223_121948.jpg
 Mineral: Unknown
 Description:
North São Paulo State
6 x 3 cm
 Viewed:  9368 Time(s)

20191223_121948.jpg



20191223_122025.jpg
 Mineral: Unknown
 Description:
North São Paulo State
6 x 3 cm
 Viewed:  9374 Time(s)

20191223_122025.jpg



20191223_121915.jpg
 Mineral: Unknown
 Description:
North São Paulo State
6 x 3 cm
 Viewed:  9373 Time(s)

20191223_121915.jpg



20191223_122115.jpg
 Mineral: Unknown
 Description:
North São Paulo State
6 x 3 cm
 Viewed:  9368 Time(s)

20191223_122115.jpg


Back to top
Reply to topic Reply with quote
Like
   

vic rzonca




Joined: 18 Nov 2008
Posts: 820
Location: MA


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 23, 2019 11:15    Post subject: Re: Black thin layer help id  

I would say it what's called a slickenside. It's a smoothly polished surface caused by frictional movement between rocks along the two sides of a fault. I collect in basalt's and have seen very large areas covered with this formation along fault zones.
Back to top
Reply to topic Reply with quote
Like
   

Robson Vieira




Joined: 05 Jan 2017
Posts: 28
Location: São Paulo

View user's profile

Send private message

PostPosted: Dec 23, 2019 12:15    Post subject: Re: Black thin layer help id  

Thanks vic. Its very cool fact. But how about the low hardness? I guess the material of the slickenside should be the same of the rock, wich is basalt in this case, that has high hardness. Maybe, the friction caused the decreasing hardness of the layer, i dont know?!
Back to top
Reply to topic Reply with quote
Like
   

vic rzonca




Joined: 18 Nov 2008
Posts: 820
Location: MA


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 23, 2019 12:36    Post subject: Re: Black thin layer help id  

I don't know all the metamorphic products that would be formed in the heat and pressure involved in that friction zone, but, some one of the learned folks here might have an idea. It could be a serpentine, hardness 3-6.
Back to top
Reply to topic Reply with quote
Like
   

David Mustart




Joined: 17 Dec 2011
Posts: 13
Location: San Francisco

View user's profile

Send private message

PostPosted: Dec 23, 2019 14:36    Post subject: Re: Black thin layer help id  

How about a pic of the opposite side of specimen?
If it is reddish brown, then possibly the shiny surface is desert varnish, a result of manganese deposition on exposed surface.

_________________
David Mustart
Professor of Geology
San Francisco State University
Back to top
Reply to topic Reply with quote
Like
   

Robson Vieira




Joined: 05 Jan 2017
Posts: 28
Location: São Paulo

View user's profile

Send private message

PostPosted: Dec 23, 2019 19:13    Post subject: Re: Black thin layer help id  

A genius idea David Mustart, thanks. Exactly as you had stated. The sample is brown at the opposite side. Would you say it solved the question? How can I detect the Mn presence to elucidate the ID?

Thanks
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 2006-2024


Powered by FMF