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Foto Fair Post your photos for friendly, non-critical feedback. This is the place to show pictures if you aren't yet ready for full-blooded critique, or simply want to share an interesting picture with other e-group visitors.

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  #1  
Old 20th October 2018
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Question Rock for ID?

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


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Old 20th October 2018
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Re: Rock for ID?

Marblelous!

No idea really
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Old 20th October 2018
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Re: Rock for ID?

Looks like Gypsum to me but I'm no expert.
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Old 20th October 2018
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Re: Rock for ID?

Veins of quartz?

It would help if we knew the region!

Jim
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Old 20th October 2018
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Re: Rock for ID?

Quartz I would go for without touching and feeling it......
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Old 21st October 2018
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Re: Rock for ID?

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Originally Posted by Jim Ford View Post
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.
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Old 21st October 2018
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Re: Rock for ID?

Portugal is big on marble so it might be an outcrop....

John
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Old 21st October 2018
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Re: Rock for ID?

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Originally Posted by Bikie John View Post
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
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Old 21st October 2018
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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
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Old 21st October 2018
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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

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Andy
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  #11  
Old 21st October 2018
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Re: Rock for ID?

Quote:
Originally Posted by shenstone View Post
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.
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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.
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Re: Rock for ID?

close up of one of the veins



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.
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Old 21st October 2018
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Re: Rock for ID?

Quote:
Originally Posted by Phill D View Post
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
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Old 22nd October 2018
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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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