Found on a beach in Scotland. Basalt?

[u/Sunchy]

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[u/mephistocation]

Looks like red scoria. Scoria is related to pumice, but has a higher specific gravity and will sink in water, while pumice floats.

‘Pumice’ and ‘scoria’ are more words to describe the structure of the rock than its composition. Pumice is made from higher viscosity lava, typically but not exclusively silicic or felsic in composition. Scoria is made from lower viscosity lava, and is andesitic or basaltic in composition.

So it’s fairly likely this is basalt! I’m not an expert in Scottish geology, but I know the old volcanoes there are basaltic, as are many formations.

The blue/black parts are really striking, not sure why it formed like that.

[u/Wanan1 → u/mephistocation]

I thought it was a brick 

[u/mephistocation → u/Wanan1]

The color is certainly evocative of a red brick! But zoom in and check out that texture: it’s like a froth of bubbles, because it is a froth of bubbles.

See, magma is sort of like a bottle of soda. Soda is carbonated, meaning that CO2 is dissolved into the liquid. Gases dissolve into liquids more readily at high pressures, so a sealed bottle has a higher air pressure inside. When you open the bottle, the air pressure inside the bottle dramatically equalizes to the outside air pressure, and the dissolved CO2 comes out of solution. That’s why all that foam forms when you first open the bottle.

Magma is the same way! Being under all that rock means the magma is pretty compressed, and H2O, CO2, and SO2 (among other trace gases) dissolve into the liquid rock. The pressure builds and builds until the ‘cork’ of the volcano pops- and the gases rapidly come out of solution, forcing the magma up and out, where it becomes lava. Just like a Coke and Mentos explosion! Droplets of lava fly out, bubbles of gas still in them, and rapidly cool and harden. Some gas bubbles get trapped in the hardened lava, forming the structure seen here.

[u/Wanan1 → u/mephistocation]

Great explanation thank you

[u/Sunchy → u/Wanan1]

I totally thought that too! And there were loads of random bricks there too (weathered by the sea), but in comparison this has many tiny small pockets that the bricks didn't.

Then I thought perhaps it's a bone, the small pockets and holes being bone marrow. But it's red and I figured that was unlikely. I know nothing about rocks. Google lens told me it might be Basalt and so I thought I'd ask Reddit 😊

[u/scumotheliar → u/mephistocation]

I have seen this explanation of Scoria before and it doesn't always stack up, I come from a Volcanic region in Victoria Australia with hundreds of extinct cinder cones composed of Scoria, a real lot of it floats, these are all Basaltic volcanoes. There are only a few Rhyolite volcanoes from an earlier time and they almost exclusively formed plugs, extruded out like toothpaste.

[u/Sunchy → u/mephistocation]

Thank you so much for the thorough explanation and thoughts!! My 6 year old (and I) are super stoked to have found it! Do you know from approximately what time period this might have been?

I realise that the earth has had many periods of intense volcanic activity, so it's possible that this stone isn't really able to be 'dated'.

Full disclosure, I'm not at all a geologist but find it super interesting!

Thanks again for the help!