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

FMF English Forum is moderated by John S. White and Peter Megaw
 

Spanish message board






Newest topics and users posts
14 Dec-22:46:18 Re: minerals of dr congo, katanga. (Roger Warin)
14 Dec-16:40:57 The mizunaka collection - quartz (Am Mizunaka)
14 Dec-15:54:05 Re: franjungle collection (Franjungle)
14 Dec-14:18:24 Re: collection of michael shaw (Crosstimber)
14 Dec-14:11:30 Re: prospecting pegmatite for schorl: need help. (Cascaillou)
14 Dec-12:18:14 Re: faden quartz crystals - (26) (Frei Hans)
14 Dec-12:17:10 Re: prospecting pegmatite for schorl: need help. (Philippe Durand)
14 Dec-10:38:53 Re: percentage of minerals known (Riccardo Modanesi)
14 Dec-04:13:50 Re: percentage of minerals known (Alfredo)
14 Dec-03:53:10 Re: percentage of minerals known (Riccardo Modanesi)
13 Dec-22:09:25 Re: percentage of minerals known (Alfredo)
13 Dec-17:59:43 Re: prospecting pegmatite for schorl: need help. (Cascaillou)
13 Dec-16:01:15 Re: prospecting pegmatite for schorl: need help. (Josele)
13 Dec-15:58:23 Re: minerals of dr congo, katanga. (Roger Warin)
13 Dec-13:53:58 Re: minerals of dr congo, katanga. (Roger Warin)
13 Dec-13:27:15 Re: prospecting pegmatite for schorl: need help. (Peter Lemkin)
13 Dec-12:54:37 Re: need help determining what this is (John Betts)
13 Dec-12:54:13 Re: need help determining what this is (Vic Rzonca)
13 Dec-12:46:02 Re: minerals sans life (Pierre Joubert)
13 Dec-12:25:09 Need help determining what this is (Billclutch)
13 Dec-11:42:42 Re: prospecting pegmatite for schorl: need help. (Peter)
13 Dec-09:32:14 Re: collection of michael shaw (Crosstimber)
13 Dec-08:13:27 Re: franjungle collection (Franjungle)
13 Dec-08:03:36 Re: collection of tobi (Tobi)
13 Dec-08:02:45 Re: prospecting pegmatite for schorl: need help. (Cascaillou)

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
36661


The time now is Dec 15, 2017 01:23

Search for a textSearch for a text   

A general guide for using the Forum with some rules and tips
What is this
  
  Index -> FOR BEGINNERS: What is it? Where is it from?
Like
4


View previous topic :: View next topic  
Author Message

Andrew Harvey




Joined: 20 Sep 2016
Posts: 9
Location: Cornwall

View user's profile

Send private message

PostPosted: Nov 22, 2017 11:54    Post subject: What is this  

Hi everyone - my first post! The photo shows a crystal on a piece of massive quartz. The field of view is about 14mm. The quartz was recovered from a small cliff fall at Pentireglaze Haven near New Polzeath, Cornwall. The bedrock in the area of the fall is a killas with occasional quartz veins. On the same stretch of coastline and fairly near is the Pentireglaze lead and silver mine. I guess the crystal is about 1mm x 0.5mm and although it has is a fine lustre, due to its size it is hard to tell if this is metallic, vitreous or somewhere in between. Is it more quartz or something else? Thank you


171122150203252005859.jpg
 Locality:
Pentire Glaze Mine, Polzeath, St Minver, Wadebridge District, Cornwall, England, United Kingdom
 Dimensions: 1mm x 0.5mm
 Description:
 Viewed:  345 Time(s)

171122150203252005859.jpg


Back to top
Reply to topic Reply with quote
Like
2
   

Pete Modreski
Site Admin



Joined: 30 Jul 2007
Posts: 605
Location: Denver, Colorado


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 22, 2017 12:34    Post subject: Re: What is this  

I got a smile out of seeing your reference to the "killas" host rocks, which is a term I haven't much seen or thought about, since I once visited mines in Cornwall, several decades ago! A classic, local-to-Cornwall geologic term.
Back to your crystal (or cluster thereof), as you say, it's hard to be certain if it is metallic or not. My guesses are, perhaps arsenopyrite if it is metallic, or something in the mica family (muscovite or chlorite) if it is not. A suggestion, under the microscope take the point of a needle and gently pick on it; see if it indents or flakes apart as a mica would, or if it is hard, then it is probably a sulfide or an arsenide.
Back to top
Reply to topic Reply with quote
Like
   

Andrew Harvey




Joined: 20 Sep 2016
Posts: 9
Location: Cornwall

View user's profile

Send private message

PostPosted: Nov 22, 2017 12:56    Post subject: Re: What is this  

It flakes, so presumably Mica. I have always wondered about testing to identify a species. I haven't done it yet because establishing hardness or streak atre likely to cause damage while ascertaining the cleavage may cause total destruction? I suppose if one has a handful of specimens, losing one for id purposes isn't too bad.

Love the site and this facility in particular. I have a couple more that I can't identify. I'll post them today but if there is a daily limit then please set them aside for another day.

Many thanks for advice
Back to top
Reply to topic Reply with quote
Like
   

Pete Modreski
Site Admin



Joined: 30 Jul 2007
Posts: 605
Location: Denver, Colorado


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 22, 2017 13:20    Post subject: Re: What is this  

No, no limits here, though we always appreciate it if someone does not post 10 or 20 unknowns one after the other!
Back to top
Reply to topic Reply with quote
Like
   
Display posts from previous:   
   Index -> FOR BEGINNERS: 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 2006-2017


Powered by FMF