The Rainbow of Rocks

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 that

encourage hematite precipitation

(red color) as well as reducing flu-

ids 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