how did this pattern form?

[BeatrizR]

Hello!

I had to drop the bike and walk through a landslide and found this crazy rock (large it was around 70 x 50 cm x 50 cm), it seems it had broken appart by the landslide. Outside the rocks just look orange (see the photo of the landslide). I consulted a friend and he suggested it is slate. However, I am curious on how this pattern could have formed. Can anyone please provide some tips?

This is on the eastern flank of the eastern Andean cordillera in Colombia.

THanks!

B.

 

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[Kray Gelder]

Welcome, BeatrizR. That's an interesting looking rock. Let me take a stab at it. The rock, without the staining, is a metamorphic taffy, of sorts. The rock, buried deeply, was subjected to the heat, pressure, and mixing, of mountain building. Hence the stirred up look, just like marble cake batter. Some of the mixture is high in what looks like iron, and after being shoved above ground as a mountain range, and fracturing from all the stress, water has been seeping through the cracks, oxidizing the iron, showing the swirl pattern. The fractured rock face collapsed, resulting in the landslide, and the exposed inner rock surface. That was a dangerous slide, probably not finished coming down yet.

 

[smokeythecat]

Kray Gelder is correct. A previously laid down rock transformed and melted by heat and pressure.

 

[BeatrizR]

Great! so it is not a slate after all!

Thanks Kray Gelder for the explanation!

B.

 

[Eu_citzen]

Probably some form of host-rock rich in iron minerals which either gave it this pattern via metamorphosis.
Or it's a outside layer related to how water tends to travel on the outcrop, oxidizing the iron minerals. I'd break of a piece and have it essayed for fun.
And that way you'll know if this is surface stuff or not.