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Identity HelpIdentification

22nd Sep 2016 15:31 UTCDaniel Wolski

Density: about 3g/cm3. Hardness: 4-6. White, greenish sratch. What is it?

http://imgur.com/a/gon7x

22nd Sep 2016 16:15 UTCHolger Hartmaier 🌟

Hi Daniel,

It looks like an igneous intrusive rock called diabase. Where did you find it? Looks like a stream or beach pebble, so it was eroded from a distant source.

Holger

22nd Sep 2016 16:17 UTCDaniel Wolski

That stone is from North of Poland, woj. Pomorskie

22nd Sep 2016 17:23 UTCHolger Hartmaier 🌟

Hi Daniel,

Unfortunately I am not familiar with the geology of Poland. In order to find out more it would be necessary to determine what sort of surficial deposit it was found in. Poland was affected by continental ice during the Ice Ages, so it is possible that glaciers could have moved material into your area from some distance. The rock appears to be gabbroic in composition, diabase is a gabbroic rock that tends to form dikes within Precambrian basement rocks, or it could come from other, possibly younger gabbroic igneous bodies in the region. I would suggest consulting a surficial geology map of your area, noting the area where you found the rock and then determining what the host material is (alluvial, glacial, marine). This may provide some clue as to where the source area was.

Each pebble has a story to tell!

Good luck!

Holger

22nd Sep 2016 18:42 UTCJakub Jirásek Expert

Definitely not diabase. Source area is the Baltic Shield, possibly Sweden. It belongs to glacial erratics and was transported by a glacier during Quaternary glaciations.

Best,

Jakub

23rd Sep 2016 01:47 UTCPaul Brandes 🌟 Manager

I believe you are confusing a diabase with a diorite, which are two totally different rocks; this is definitely not a diabase rock. To me, it appears more like an epidotised granite which is why it is so green.

23rd Sep 2016 02:03 UTCHolger Hartmaier 🌟

I don't see a lot of quartz in this rock, so I don't agree it is a granite. if S.G. determination is correct, it looks too dense for a granite too. I see mainly plagioclase feldspar (greenish) and mafic minerals, so it is in the dioritic to gabbroic family of igneous intrusives. Diabase is a textural term, but diorite works for me too. Need to have mineralogy really to make an accurate determination- really just guessing from a series of photos.

24th Sep 2016 03:29 UTCGregg Little 🌟

The green alteration, actually a dull apple green as it is a transported pebble, looks very much like the epidote alteration of feldspar intergrown with the darker mafic minerals which, as earlier stated, seems to fall with in the gabbro group.

24th Sep 2016 13:39 UTCErik Vercammen Expert

Epidote is a calcium-aluminium-silicate with OH-groups: if (hot) water reacts with calciumrich feldspars, it is a common product. Those feldspars are typical for basic rocks like gabbro and diorite.

24th Sep 2016 15:12 UTCDaniel Wolski

What should I do to help with identification? :-)

24th Sep 2016 16:53 UTCD. Peck

Daniel, aside from taking it to a university geologist, I don't think there is much else you can do. Since it is a rock, not a mineral, analysis would normally be done by cutting a thin-section from it and observing it under a polarizing microscope. You could have that done, but I am not sure it is worth it. If I were you, I would accept the comments above, and keep the pebble to remember your trip or time in Northern Poland.

24th Sep 2016 19:09 UTCDaniel Wolski

Thank you all for the answers! Have a nice evening! :-)

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