Opalized Wood

Wood material is often preserved in the rock record. Most commonly it is preserved as petrified wood, which is wood replaced with small grains of quartz. This is truly a replacement, unlike fossilized bones where the original bone is usually still present and minerals grow around it. Occasionally, opal can replace the wood instead of quartz. Opal and quartz (or chert/jasper) are very similar. Opal is a hydrated form of silica, and this hydration gives the opal a gemmy appearance and cause a play of colors called fire.

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