How to Identify Petrified Wood: What to Look For and Home Tests

Petrified wood is wood replaced by silica cell by cell, so it keeps growth rings and grain while testing as hard as quartz. The properties that identify Petrified Wood — color: Impurities (iron, carbon, manganese) color the quartz, producing a 'rainbow of colors.'; cleavage or fracture: Hard and brittle; fractures readily under stress, sometimes breaking as cleanly as a glass rod. For a rock, texture and grain size matter more than any single hardness number.

• Composition test: petrified wood is made up of almost solid quartz, so its Mohs hardness is close to quartz's (it can scratch glass); however, no explicit Mohs value for petrified wood itself was found for this table, so it is left blank.

Petrified Forest National Park in Arizona is the most famous North American locality.

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.

Formation process: buried wood is slowly infiltrated by silica dissolved out of volcanic ash, which crystallizes within the cell structure and gradually replaces the original organic material.