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Earth Notes: Jeweled Trees

Southwest: American

No one expects to see trees that look like jewels in the high desert of Arizona. But that’s exactly what visitors find in the Petrified Forest National Park – ancient logs preserved for millennia by a process that transfigured them into rare and beautiful stones.

More than 200 million years ago, Earth’s continents were squashed together in one giant landmass called Pangea. Enormous reptiles prowled through fields of ferns, beneath trees that towered 200 feet tall. When those trees fell, rivers swept the logs into piles and buried them in mud. Volcanic ash rained down, preserving the wood from decay. Over time, minerals dissolved in water began to seep into the wood… especially silica, which crystallizes into quartz, a clear or smoky gem.

Trace amounts of other minerals add a rainbow of colors to the petrified wood. Iron creates swirls of red, orange, or pink. Carbon and manganese add streaks of black. Deep green comes from copper or chromium, which is the same mineral that gives emeralds their hue. There are even pockets of yellow citrine and purple amethyst, colorful varieties of quartz.  

The fossilized wood still holds the texture of bark and knotholes. This treasure trove might have stayed hidden forever. But when the Colorado Plateau began to rise 60 million years ago, erosion exposed the logs. Many more still lie hidden beneath the surface, along with the fossils of Triassic crocodiles and early dinosaurs.

Today the petrified wood within the park is protected by law. Hundreds of thousands of visitors each year marvel at living trees transformed into shining jewels.