Identify a rock.

[Writhing]

Just wondered if anyone can identify what this is. My brother-in-law picked it up from a beach in New Zealand. After admonishing him for removing minerals etc.........we wondered what it was.

(teaspoon is for scale)

[Lynchie999]

I don't think those oval type shapes are fossils or anything, looks like "weathering" from water, drips from somewhere and the rock has been moved around slightly giving loads of indents...

Is it black inside ?

Probably some intrusive granite type rock... see if its crystalline ... ?? If your that bothered smash it open, the surface colour most likely isn't the actual colour of the rock ? can't really tell form the photo ...

edit - might be some sort of flint nodule, with the white stuff its "parent" limestone type rock ?

[JuniorD]

Looks like a Tewhatu-mori. A "Tapu" item, that supposed brings erectile dysfunction to anyone who takes one.

[Toltec]

Looks somewhat like a pebble eroded by molluscs, though the holes I've seen tend to be more circular.

[rev-erend]

Looks like sedimentary rock. Not chalk but something similar with more pressure as it looks harder.

[Zad]

My first thought was a volcanic rock with holes caused by venting gas, or perhaps sedimentary tufa that has been bashed around and smoothed, but on closer inspection the "holes" do seem to be more like surface gouges. It looks like fossilised Blu-tak

Is it chalky? Dull sounding or hard when its tapped?

[Beati Dogu]

Looks like flint to me.

[Writhing]

Its surprisingly heavy for its size. I wondered about volcanic but wondered if that would be black. It seems very hard. I can't scratch it.

[Lynchie999]

smash it open! what are those dark spots on it ??

[mko9]

Whatever it is, I wouldn't take it for granite

[Toaster]

Blue in a mineral could indicate it has some copper content, why not take it to your local mineral rock club

[Lynchie999]

mko9 said:

Whatever it is, I wouldn't take it for granite

I was generally hypothesising.... being in NZ and all....

I don't think the surface colour is its actual colour ? ... the white looks like some deposit...

as in... its "well 'ard" and hasn't been weathered too much! OP, what are the dark grey blobs ? thats looks like its natural colour ?

Edited by Lynchie999 on Tuesday 27th February 17:47

I'd go for flint nodule.... the white is its parent rock (limestone / chalk of sorts) the indents are impressions from the shells from the limestone....

Edited by Lynchie999 on Tuesday 27th February 17:49

[BigJonMcQuimm]

Maybe this?

http://www.mcrocks.com/ftr06/AdamsMarch06.html

[Toaster]

BigJonMcQuimm said:

Maybe this?

http://www.mcrocks.com/ftr06/AdamsMarch06.html

Good Call, it looks like it could be something like Leland Bluestone https://www.google.co.uk/search?client=safari&...

Edited by Toaster on Wednesday 28th February 07:32

[Toltec]

Toaster said:

Good Call, it looks like it could be something like Leland Bluestone https://www.google.co.uk/search?client=safari&...

Edited by Toaster on Wednesday 28th February 07:32

Similar, but the cavities in that look more like the outgassing you would expect in a smelting process and they are local to Michigan. The OP's could be a product of an industrial process though, I once confused one of my classmates also studying geology when I showed him a chunk of scale from the bottom of a hot water cylinder.

[Toaster]

Toltec said:

Similar, but the cavities in that look more like the outgassing you would expect in a smelting process and they are local to Michigan. The OP's could be a product of an industrial process though, I once confused one of my classmates also studying geology when I showed him a chunk of scale from the bottom of a hot water cylinder.

I know nothing about geology but interestingly you mention outgassing would or could a volcanic outgassing cause a similar substance to be produced?

[Toltec]

Toaster said:

I know nothing about geology but interestingly you mention outgassing would or could a volcanic outgassing cause a similar substance to be produced?

Pumice and scoria for a start, though they are more extreme examples.

ETA- I did an 'O' level in it nearly forty years ago so my knowledge is limited

Edited by Toltec on Wednesday 28th February 15:22

[Toaster]

Toltec said:

Pumice and scoria for a start, though they are more extreme examples.

Interesting, there are some colourful ones here https://www.shutterstock.com/image-photo/pumice-st...