The Rainbow of Rocks, The Wave

"Sandstone Coloration is:

• A function of varying amounts of iron (mineral hematite - Fe) that imparts red color.

• Initially red, soon after sand grains are deposited and buried.

•Red where thin scattered films of hematite coat sand grains, and white where the thin films of hematite have been removed by bleaching.

• Facilitated by how easily fluids can move through a sandstone due to different textures of the sandstone (e.g., how loosely or tightly sand grains are packed together).

•Variable even on a scale of fractional inches where thin red

layers alternate with white layers.

This is again a function of microscopic textures in the sandstone.

•Affected by oxidizing fluids thatencourage hematite precipitation (red color) as well as reducing fluids that bleached the sandstone by removing the hematite (white color).

•A property that may have changed over time and involves

fluids and processes that occur over tens of millions of years. "

 

Rainbow of Rocks

Mysteries of Sandstone Colors and Concretions

in Colorado Plateau Canyon Country

by Marjorie A. Chan and William T. Parry

Dept. of Geology and Geophysics

Done