FOSSIL WOOD

Araucarioxylon arizonicum
225 million years
Arizona, USA

This fossil wood example from the southwestern US state of Arizona is of astonishing beauty. In 1988 the Arizona state legislature designated the petrified wood of Araucarioxylon arizonicum, a prehistoric conifer, as an Arizona state fossil. Arizona is famous for its vast petrified forest, part of which lies within the bounds of the Petrified Forest National Park.

During the Late Triassic period, approximately 225 million years ago, Northern Arizona had a tropical climate that supported a vast forest of conifer trees. The majority of the trees were of the species Araucarioxylon arizonicum, which grew up to 200 feet (61 m) tall with a trunk up to 5 feet (1.5 m) thick. It likely would have resembled a modern pine tree. Occasionally fallen trees would become buried in sediment and volcanic ash. Due to its rapid burial and the lack of oxygen, the wood did not decay as it would if it had remained on the surface. Silica and other minerals present in the ground water seeped into the porous wood over many years. This caused the cellular structure of the wood to become crystallised and turned it into a fossil.

The rainbow coloration with vibrant hues of reds, yellows and purples is typical for petrified fossils from Arizona. It is made up of almost solid quartz, like a giant crystal, and sparkles in the sunlight as if it were covered with glitter. The rainbow colours are produced by impurities in the quartz, such as iron, arbon or manganese. Purple amethyst, yellow citrine, clear quartz and smoky quartz have formed here into a wonderful piece of natural art.