I recently visited a quarry site and brought home a rock sample that had two clusters of cubic crystals on its surface. I am unsure what the mineral is, I think it may be fluorite but I am not certain. The crystals are light brown and rather small.

The quarry is roughly 50m deep and most of the rock is pelite and schist with significant amounts of quartz throughout.

If any pictures are unclear or more information is needed I will edit this question to suit as best I can.

One of the crystal formations.

The other crystal formation.


closed as off-topic by Leukocyte, Fred, uhoh, Semidiurnal Simon, Gimelist Sep 1 at 7:39

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    $\begingroup$ Try some tests: Lick it - probably not halite but easy enough to test to see if it tastes like salt. Try to scratch with a pin or a knife - fluorite has a hardness of 4 so it should scratch easily. Go ahead and put some acid on it and the surrounding white material to see if there is any calcite. The crystals do mostly look cubic but it is always good to rule things out. Can you tell us where this was found? What were they quarrying? $\endgroup$ – haresfur Dec 29 '16 at 22:41
  • $\begingroup$ @haresfur I found the rock in a pile with a mixture of other rocks and gravel from around the quarry. The purpose of the quarry is to provide material for road building so workers aren't searching for any specific minerals as any rock mined is crushed and used in tarmac. $\endgroup$ – The Garage Chemist Dec 30 '16 at 12:37
  • $\begingroup$ My guess is fluorite. Is the lustre a bit oily, once you clean it from dirt? Is the hardness appropriate for fluorite? It could be some exotic mineral (there are almost 5000 minerals out there after all), but fluorite would be my best guess. $\endgroup$ – Gimelist Dec 30 '16 at 23:46

From purely physical examination from the photo, crystal morphology and luster appears most likely be calcite (85% chance). You would need an HCL acid test to confirm. Less likely, the mineral might be fluorite (10% chance).

If you can provide a specific location, country, state\province, county, there is a significantly smaller probability that the mineral might be something more unusual than calcite or fluorite (5% chance).

I have collected calcite specimens that have the exact shape and luster as shown in the photo.

  • $\begingroup$ I found the sample in west County Tyrone, Northern Ireland. I don't have a wide knowledge of the occurrence or rarity of certain minerals in this area unfortunately. I will certainly look into testing a sample of the crystals with hydrochloric acid. I will post the results once I have done this. I'm not sure if this will help but I also shone a uv light on the sample for a prolonged period of time and the mineral glowed a pale white/yellow colour that quickly vanished. $\endgroup$ – The Garage Chemist Jan 15 '17 at 21:14
  • $\begingroup$ Calcite and fluorite can both fluoresce white $\endgroup$ – Gary Kindel Jan 16 '17 at 13:09

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