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Can somebody please help. I found this rock on the beach in the south of England. It seems to have a number of small shards of what look like crystal or glass spread around it whilst the rock itself has an overall sheen. The pictures don't do it justice. There is also a copper/bronze coloured ore attached to it.

The bronze coloured stuff is hard. I am struggling to scrape anything of it the whole thing seems pretty solid. I can make a scratch mark on the bronze coloured bits but the grey part doesn't mark. To be honest I'm damaging my knife more.

After scraping for some time I find that the small amounts of lighter coloured bronze comes away with a grainy texture. Although I'm not an expert I presume this to be sand which has accumulated over time and compacted to make it hard. The larger amounts of dark bronze do not, this is a lot tougher. When scraping at it my knife seems to leave a kind of silver mark, which fades when rubbed. It's as if the knife is somehow scraping off onto the rock?

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closed as off-topic by user12525, Gimelist, Fred, BillDOe, Jan Doggen Aug 26 at 7:40

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions about rock identification requests are off-topic. For more information, see the announcement on meta." – Community, Gimelist, Fred, BillDOe, Jan Doggen
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Welcome to Earth Science Stack Exchange! Could you follow the directions in: meta.earthscience.stackexchange.com/questions/124/… $\endgroup$ – arkaia Jan 6 '17 at 22:13
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    $\begingroup$ Try to scratch the white-grey stuff with a knife. Can you make a scratch in it? Then, scratch the bronze stuff with a knife as well. Can you flake some off it? Are the flakes scaly, or flat? Is the bronze coloured stuff soft? Can you remove some of it with your fingernails? Note that you might need to use a magnifying glass to see any shape of the stuff you scratch off it. $\endgroup$ – Gimelist Jan 7 '17 at 6:11
  • $\begingroup$ Thank you for the reply. The bronze coloured stuff is hard. I am struggling to scrape anything of it the whole thing seems pretty solid. I can make a scratch mark on the bronze coloured bits but the grey part doesn't mark. To be honest I'm damaging my knife more $\endgroup$ – Libbyjack12 Jan 7 '17 at 18:10
  • $\begingroup$ After scraping for some time I find that the small amounts of lighter coloured bronze comes away with a grainy texture. Although I'm not an expert I presume this to be sand which has accumulated over time and compact to make it hard. The larger amounts of dark bronze do not, this is a lot tougher. When scraping at it my knife seems to leave a kind of silver mark, which fades when rubbed. It's as if the knife is somehow scraping off onto the rock? Whatever it is I'm having so much fun examining it I think I may have found a new hobby. $\endgroup$ – Libbyjack12 Jan 7 '17 at 19:30
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It is a large block of quartz or chert, broken off from a rock called conglomerate. Your knife doesn't scratch it because quartz is harder than knives.

When scraping at it my knife seems to leave a kind of silver mark, which fades when rubbed. It's as if the knife is somehow scraping off onto the rock?

Basically, yea.

The bronze stuff around it is lithified sand, that is probably made out of more quartz, just smaller. The bronze colour in your case comes from staining of the sand by iron oxides or clays (which is what usually makes sand brown). It's possible that some of it has metamorphosed a bit to form some micas, which give it a characteristic sheen. In some of the pictures you can see some kind of layering in the brown stuff, which means it's a sedimentary rock.

Welcome to geology, it's fun. There are many websites about rock identification and how to identify various components. I would recommend amateur websites and not Wikipedia which can get too technical (and pretty much useless if you don't know it) at times.

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    $\begingroup$ Thank you so much. I've had it for a year now so to finally know what I have is amazing. I'm going to spend the rest of the night filling my search history with rock identification and geology! $\endgroup$ – Libbyjack12 Jan 7 '17 at 21:07
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    $\begingroup$ @Libbyjack12 great to hear! Don't forget to upvote and accept the answer by pressing the up arrow and the V next to it. :) $\endgroup$ – Gimelist Jan 7 '17 at 21:18
  • $\begingroup$ @Michael Thanks for the suggestion about having amateurs not default to Wikipedia. Do you have any major recommendations as to what other sites are best for amateurs? $\endgroup$ – theforestecologist Feb 18 '17 at 19:08
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I'd say it was a weathered clast of quartz vein possibly with staining and/or some fragments of the vein host rock. The crystal structure to me rules out this being chert or sedimentary quartz in origin. The weathered state doesn't though automatically mean it is re-worked from a conglomerate.

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Not all metamorphic rocks have been 'completely' metamorphosed. Sanstones that are heated and under great pressure become quartzites, and shales slate for example, but if the heat or pressure is insufficient, the result can be veins of partially metamorphosed rock.

It looks like you've a good example of this. Some of the rock completely melted, and recrystalised, whilst other bits were only partially melted, leaving layered pieces still 'floating' in the substrate. As mentioned, the presence of iron in the sand is evident. The fact is, this rock is not a single cohesive piece of chert, quartz or granite, but has some bits of several minerals - - such as mica, quartz and I'd guess calcium plagioclase, which is white. These three minerals make up a type of granite. So you may have a Frankenstein rock - - made up of many minerals, but not baked enough or under great enough pressure to completely transform it, and not the right percentages of mica to plagioclase to quartz to be a 'true' granite.

I'm guessing. My education was in geomorphology, not strictly geology, so a bit more high level than the geologists here...

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  • $\begingroup$ Not any igneous rock. It is quartz. Impossible to know if it is a metamorphic quartzite, or a sedimentary rock: a breccia or an altered block of quartz. $\endgroup$ – user12525 Jul 18 at 9:06

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