Reduction Spots and Bands

The red sandstones were laid down by seasonal braided streams in a desert environment. The beds were originally red. After burial, migration of ground water caused reduction of some ferric oxide (Fe₂O₃) to ferrous oxide (FeO), which is slightly soluble. Leaching of the reduced iron caused the colour to change to green, or colourless.

• Look for any evidence that would tell you whether the beds were originally green and have been later turned red, or were originally red and later turned green.

Notice the colour change along cracks in this picture.