Sibley rock display: rhyolite tuff

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Sibley's rock collection: rhyolite tuff

Rhyolite tuff:
lithified ash.

This rock is displayed in “Sibley's Geological Treasures” collection on the roofed patio of the visitor center in the Robert Sibley Volcanic Regional Preserve. The above caption is the same that is given on-site (June 11, 2012).

Rhyolite is a light-colored volcanic rock composed of alkali feldspar, silica and minor amounts of mafic minerals (magnesium- and iron-rich minerals).

Rhyolite tuff is consolidated volcanic ash, containing rhyolite constituents and pumiceous, glassy fragments (glass shards).