Araucarioxylon arizonicum (the state fossil of Arizona) is an extinct conifer of the late Triassic, a time when what is now Petrified Forest National Park was a low, near equatorial, plain. Mountain streams, flowing to the sea, carried volcanic ash high in silicon bound as orthosilicic acid and as crystals of silicon dioxide, quartz. Trees deposited in rivers were covered in sediment, their tissues were saturated, and tubes of xylem and phloem provided easy access to deep within the plant. The rest is history. Negatively charged crystals of quartz accumulated in cells and cast organic tissue in rock – preserving specimens in minute detail. The colors in petrified wood are dependent upon mineral ions bound to quartz. Below, relatively pure quartz is white, iron oxides may be responsible for reds and browns, and manganese may be associated with hues of pink and orange.

8 thoughts on “Petrified

  1. David – you are superb writer and photographer, and your explanation is so easy to follow. Thank you for being a great teacher. I will again say that you should put all of the photographs/writings together in a book.

    • You know, since you first mentioned it, the thought has made its way into my consciousness – and then back out again – on several occasions. Not that I have done anything about it – but I have thought about it. What vehicle would you suggest? Something like Lulu? If so, I have found that cumbersome.

  2. I didn’t know about state fossils! I just can’t wrap my head around such long time scales … and the fact that they can be so unassumingly and beautifully summarised in a colourful piece of rock!

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