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Brown gem found in smooth white rock very fine smooth almost shiny with clean breaks and a bluish tinge on breaking.

Northern Ireland just south of Bangor on the North Down coast.

Cheers!! Andy

enter image description here

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  • $\begingroup$ Welcome to Stack Exchange Andy! For posts like these, it helps a great deal to add as much information as possible along the lines of stuff suggested in this rock identification question guide $\endgroup$ – JeopardyTempest May 28 '18 at 5:32
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    $\begingroup$ I leave also an interesting link. Geological Ireland survey has arcGIS integrated. Tick in bedrock 500k, the zone is cartographied. dcenr.maps.arcgis.com/apps/MapSeries/… $\endgroup$ – user12525 May 28 '18 at 12:40
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    $\begingroup$ Is the white rock almost dusty to touch? It looks like chalk to me. Can you scratch the orange crystal to see how hard it is? $\endgroup$ – bon May 30 '18 at 9:05
  • $\begingroup$ Andy if you read this it is important for us some extra information $\endgroup$ – user12525 Jun 2 '18 at 15:40
  • $\begingroup$ You found it at the beach? We need please that you put the piece on a table or so, and very very close you make a picture focused. At smartphones you are abble to touch the object to focus it. We need to have a better view of the white rock $\endgroup$ – user12525 Jun 2 '18 at 15:43
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Since it seems like the OP isn't going to reply to my requests for information I'll take a stab at this based on what I can see.

The white rock has a pitted and slightly dusty appearance that looks very much like chalk to me. The BGS description for the Ulster White Limestone which lies nearby shows that it contains chalk:

Principally limestones (hardened chalks) with subordinate flint, marl, sponge bed, hardground, conglomeratic and fossil acme bands, with glauconite grains where formations become condensed over structural highs.

As for the orange crystal embedded within the chalk, it looks like it is a nodule that has grown in the chalk because it has rounded edges and seems to radiate out from a central point. I'm not really an expert on this type of thing but my best speculation is halite (which is very easy to test just by licking it!). Someone will probably come along and correct me though. This paper suggests that diagenesis involved marine fluids so I guess halite is an option, though it doesn't mention it there.

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  • $\begingroup$ Maybe. Then transported too. It is true it looks like a chalk, but I thougth the orange mineral shoul have a magmatic origin. I leave a map with that formation at the zone. earthwise.bgs.ac.uk/images/1/1d/P947855.jpg $\endgroup$ – user12525 Jun 1 '18 at 16:00
  • $\begingroup$ @Gimelist: what can be the orange mineral? I think bon's location of the chalk is correct, but maybe related with extrusive system and then transported to Banglor's coast. $\endgroup$ – user12525 Jun 1 '18 at 21:42
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    $\begingroup$ @Universal_learner this is either silica (citrine-like quartz, chalcedony, chert), calcite, or gypsum. Less likely but possible: halite, barite, aragonite, dolomite, or any other sedimentary mineral. Without any more information (hardness, reaction to acid), it is not possible to say. $\endgroup$ – Gimelist Jun 2 '18 at 11:57
  • $\begingroup$ I think we are close. But we'd need to be sure it is Ulster White Limestone Formation. Silica rich environment. eg page 9 figure 3. nora.nerc.ac.uk/id/eprint/19482/1/CR09096N.pdf $\endgroup$ – user12525 Jun 3 '18 at 12:29
  • $\begingroup$ @Universal_learner We cannot be sure of anything from the information given. I am merely suggesting what seems like a likely source for chalk in this area. $\endgroup$ – bon Jun 3 '18 at 13:08
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Spessartite garnet can be easily identified since its high in iron content making it magnetically susceptable.use a neodynium to find out. I have to say that the source is metamorphic for this type of gemstone. I have similar examples of spessartite in the parent rock but not as large as yours. It looks gemmy which if faceted correctly could make it worth a good sum.

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  • $\begingroup$ Taking a look at this graphs, he migth have found it at Hawick or Gala Group that are turbidites. Belfast zone has permian basement I think (Guadalupian and Lopingian Epoch). There is also Leadhill Supergroup with conglomerates. I have read the zone is Mn rich geochemistry talking. There are riolites associated with basalts too(Tardree Rhyolite Complex) .earthwise.bgs.ac.uk/images/5/5e/P947802.jpg $\endgroup$ – user12525 May 30 '18 at 6:44
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    $\begingroup$ No, spessartine (and garnets in general) are not magnetic enough to be identified with a magnet. $\endgroup$ – Gimelist Jun 2 '18 at 11:55
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Edited 02/06 Currently, our guess is the rock and the mineral are both sedimentary.

The orange color of the mineral makes think that the mineral could be spessartine, a Mn-rich mineral of garnets group.

Spessartine is found in four main environments:

  • Granitic plutonic rocks
  • Rhyolitic volcanic rocks.
  • Metamorphic rocks (pelithic protolites)
  • Pegamtites (associated with igneous rocks)

There is another brown/orange mineral called zircon. It is found in several magmatic environments. Zircon is a hard an persistent mineral that is also found on sedimentary deposits.

We all think about the orange mineral, and question about the rock that contains it has interest for the identification

The geology of the zone, and the place where it was found can clarify the origin of the mineral:

enter image description here

Geology of North Ireland. Bedrock Geology 100K. Geological Survey Ireland.

Andy comments that he found it at the south of Bangor, on the coast. Green unit corresponds with Gala group, Silurian turbidites. Probably that piece would have not survive to turbidite currents, but there is a sugests it migth be a diagenetic carbonate nodule.

The zone of yellow color corresponds, if I am not wrong, with Permian basement that does not reach the metamorphism.

What I bet is the white rock is a rhyolite,and comes from Paleogen Tardree Rhyolite Complex.

enter image description here

Antrim Lava Group. BGS Earthwise - British Geological Survey

If this piece was found at the coast, it migth be formed in recent Tertiary rhyolitic lavas, and a river transported it to the coast.

Anyhow, I will need to confirm the white rock is a rhyolite to validate my hypothesis.

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  • $\begingroup$ There is zircon at that complex. I am horrible identifing but I would say my hypothesis is true and this is a transported piroclast of rhyolite with zircon inside.sciencedirect.com/science/article/pii/S000925411100194X $\endgroup$ – user12525 May 30 '18 at 11:03
  • $\begingroup$ I very much doubt that this is a zircon. Zircons that big are very rare. All the ones analysed in the paper you linked are <0.5 mm in size. $\endgroup$ – bon May 30 '18 at 12:09
  • $\begingroup$ I didn't see any link to garnets at that extrusive system. I am not good identifiyng and it is difficult to everybody with no more info. I think what we need to know is location and what is the white rock. $\endgroup$ – user12525 May 30 '18 at 12:25

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