sedimentary
Sandstone (specifically Double Arch in Arches National Park)
Entrada Sandstone
Hardness: 6-7 (based on quartz content); Color: Red, orange, tan; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Composition: Predominantly quartz grains with iron oxide (hematite) cement.
- Hardness
- 6-7 (based on quartz content)
- Color
- Red, orange, tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (based on quartz content); Color: Red, orange, tan; Luster: Dull/Earthy; Structure: Clastic, fine-grained; Composition: Predominantly quartz grains with iron oxide (hematite) cement.
Formation & geological history
Formed during the Jurassic period (approx. 150-200 million years ago) from ancient sand dunes. The arches are created by differential weathering and erosion, specifically salt tectonics and frost wedging.
Uses & applications
Primary use is tourism and aesthetic conservation. Sandstone generally is used in construction as building stone and grit for grinding.
Geological facts
Double Arch is a 'pothole' arch, formed by water erosion from above rather than side-to-side. It was a filming location for the opening scene of 'Indiana Jones and the Last Crusade'.
Field identification & locations
Identify by its distinct reddish-orange hue and cross-bedding layers. Found commonly in the Colorado Plateau. Collectors can look for small tumbled samples or decorative slabs.
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