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-   -   Rock for ID? (http://e-group.uk.net/forum/showthread.php?t=49038)

Invicta 20th October 2018 07:44 PM

Rock for ID?
 
Any geologists out there that can help ID this mineral in the rock strata please?


http://e-group.uk.net/forum/picture....pictureid=2909

Walti 20th October 2018 08:01 PM

Re: Rock for ID?
 
Marblelous!

No idea really ;)

Phill D 20th October 2018 08:37 PM

Re: Rock for ID?
 
Looks like Gypsum to me but I'm no expert.

Jim Ford 20th October 2018 09:37 PM

Re: Rock for ID?
 
Veins of quartz?

It would help if we knew the region!

Jim

MJ224 20th October 2018 10:47 PM

Re: Rock for ID?
 
Quartz I would go for without touching and feeling it......*chr

Invicta 21st October 2018 06:28 AM

Re: Rock for ID?
 
Quote:

Originally Posted by Jim Ford (Post 460534)
Veins of quartz?

It would help if we knew the region!

Jim

Region is south west Portugal on the coast. I guess it is a hard mineral else the sea would have washed it way. Quartz sounds best bet.

Exact location: Praia dos Buizinhos, Porto Covo. A tiny beach: lots of pictures on the web nobody else seems interested in those white veins in the rocks though of which there were many.

Bikie John 21st October 2018 08:19 AM

Re: Rock for ID?
 
Portugal is big on marble so it might be an outcrop....

John

Jim Ford 21st October 2018 09:02 AM

Re: Rock for ID?
 
Quote:

Originally Posted by Bikie John (Post 460544)
Portugal is big on marble so it might be an outcrop....

The sharp, unweathered fractures suggest something much harder than marble.

I've see loose lumps of quartz like that on the plateaus of the Cairngorms. They always reminded me of coconut ice at a distance!

Jim

drmarkf 21st October 2018 12:53 PM

Re: Rock for ID?
 
I'm no geologist, but it does look like quartz to me, especially the way the minerals in the rocks above and below have stained it and the way it seems to be arranged in an overall rough crystalline structure.

Have a skim down some of the images here: https://www.google.co.uk/search?q=qu...=1252&bih=1042

shenstone 21st October 2018 04:41 PM

Re: Rock for ID?
 
I was a geologist so I'll stick my neck out

I do think it is quartz veining in a mudstone

I am not sure of the scale which is why geologists always include something of known size in the picture - good tip a coin is known size and if you have nothing better a lens cap which is not known size, but allows a sense of overall scale from huge to medium etc. Some examples like this in my website http://www.shenstone.me.uk/galleries...nts/index.html

Back to yours. I think at the scale I think it is that I would see the crystaline structure of gypsum or calcite

Re the vein's there is a slight curve to them. When you see veins all with S type curves you can tell which way the pressure has come from - not enough to tell direction of strain from in this picture IMO

Hope that helps

Regards
Andy

Invicta 21st October 2018 06:44 PM

Re: Rock for ID?
 
Quote:

Originally Posted by shenstone (Post 460632)
I was a geologist so I'll stick my neck out

I do think it is quartz veining in a mudstone

I am not sure of the scale which is why geologists always include something of known size in the picture - good tip a coin is known size and if you have nothing better a lens cap which is not known size, but allows a sense of overall scale from huge to medium etc. Some examples like this in my website http://www.shenstone.me.uk/galleries...nts/index.html

Back to yours. I think at the scale I think it is that I would see the crystaline structure of gypsum or calcite

Re the vein's there is a slight curve to them. When you see veins all with S type curves you can tell which way the pressure has come from - not enough to tell direction of strain from in this picture IMO

Hope that helps

Regards
Andy

Thanks Andy,

Valid point about scale. Each white vein was about an inch to inch and half wide in old money (2.5 cm- 3.75 cm). So the whole photo below must be about 9 inches high.

From memory the veins ran the whole length of the exposed cliff face and waved up and down quite regularly. I should have taken a wide angle shot of the whole cliff face as well.

I always thought quartz was clear but reading on the web there are lots of coloured quartz and white quartz is called milky quartz.

Phill D 21st October 2018 07:08 PM

Re: Rock for ID?
 
It will be interesting to know when you get someone who can be sure but it doesn't look like the 6 point angular nature of the quartz crystals I've seen before. Did you get a sample? if so then try scratching it with a knife. If it's quartz it wont scratch as it's harder than the knife blade.

Invicta 21st October 2018 07:50 PM

Re: Rock for ID?
 
close up of one of the veins

http://e-group.uk.net/gallery/data/5...te_veins_3.jpg

not sure if it shows any more info, the white veins didn't have any crystalline structure as such. But then they are washed by the sea twice a day so must be very hard.

Jim Ford 21st October 2018 08:11 PM

Re: Rock for ID?
 
Quote:

Originally Posted by Phill D (Post 460647)
It will be interesting to know when you get someone who can be sure but it doesn't look like the 6 point angular nature of the quartz crystals I've seen before. Did you get a sample? if so then try scratching it with a knife. If it's quartz it wont scratch as it's harder than the knife blade.

The quartz is a amorphous form, rather than crystalline. Almost all the quartz I've come across is amorphous eg. the flint we have in Hertfordshire.

Jim

shenstone 22nd October 2018 06:34 PM

Re: Rock for ID?
 
I'm sure - Quartz

As you say it's amorphous, Gypsum would have been fibrous or "sugary" and Calcite would have showed rhombic cleavage

Flint is as noted by Jim another form of amorphous quartz. that basically means that it has no, to "very small" crystals and with the white form you have in these pictures it's going to be "very small"

Nice pure larger crystals (from a few mm across to huge) are the glassy form that PhillD is used to looking at

Regards
Andy


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