Close-up of silicified limestone (tripoli) below karstic passage in Worland Limestone

Portion of a limestone lens altered to tripoli chert. Acidic rain water
infiltrated the rock, becoming saturated with silica leached from clay
minerals in the shaly matrix. When the original carbonate dissolved,
chert precipitated in its place. Because this form of chert is porous,
mineral-laden water continued to pass through it, bringing the iron
oxide that stained it peach and maroon. The two fragments of tripoli
just to the right of the hammer head are shown in the close-up. They
came from an area near the very center of the photograph. X-ray
analysis shows this material to be nearly 100% silica.

View close-up

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