The oldest widely accepted rock on Earth is a metamorphic rock called gneiss, specifically the Acasta Gneiss in northwestern Canada.

Quick Scoop

  • The Acasta Gneiss is a banded gneiss , a high‑grade metamorphic rock.
    Scientists date parts of it to about 4.03 billion years old.
  • Gneiss forms when earlier rocks (often igneous like granite or basalt) are intensely heated and squeezed deep in the crust, rearranging minerals into light–dark bands.
  • Some even older Earth materials exist as tiny zircon crystals in younger rocks, but those are minerals, not whole rocks, so the Acasta Gneiss remains the classic “oldest rock” example.

In short: when people ask “what type of rock is the oldest rock on Earth?”, the usual answer is a metamorphic gneiss (the Acasta Gneiss).

Information gathered from public forums or data available on the internet and portrayed here.