Why Petrified Logs Look Like They’ve Been Cut (The How and The Why)

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Exploring the Reason Behind Petrified Wood’s Cut Appearance

Petrified logs are a fascinating natural phenomenon. They’re ancient trees that have been transformed into stone over millions of years, and can be found all over the world. But some of the most famous and most impressive specimens are located right here in the Unites States, inside the Petrified Forest National Park in Arizona.

If you’ve seen these petrified logs, then you’ll have noticed that one of the most striking features of these logs is that they look like someone cut them with a saw.

If you’ve asked yourself why they look that way, you’re not alone. Many people wonder why the petrified logs look like they’ve been cut.

Petrified logs that appear to have been cut

The answer lies in the process of petrification. Petrified wood is mostly silica—quartz, which is very hard but also very brittle. After petrification, but while the logs were still encased in matrix, the logs cracked under stress. It’s these cracks are what give the logs their distinctive appearance.

While the process of petrification is fascinating in itself, the mystery of why the petrified logs look like they have been cut adds another layer of intrigue.

Related: The “Conscience Pile”: A Fascinating Display of Repentance at Petrified Forest National Park

Multiple stress fractures visible in this petrified log

Why Do Petrified Logs Look Like They Were Cut?

Weathering and Erosion

One reason why petrified logs look like they were cut is due to the effects of weathering and erosion. According to Arizona Highways, the movement and erosion of the land caused the logs to break. The inner surfaces where they’ve broken are flat because quartz doesn’t break neatly across its crystal faces, so instead, it snaps across the log’s shortest area across. This snapping effect is similar to when you snap a piece of chalk.

Mineralization Process

Petrified wood is mostly silica-quartz, which is a hard and brittle mineral. The logs are very hard, with a rating of 7.8 on the Mohs hardness scale. After petrification, but while the logs were still encased in matrix rock, the logs cracked under stress. As a result, the logs fractured evenly along the tree trunk, giving the appearance of logs cut with a chainsaw. This process is explained by Petrified Forest National Park.

Fossilization Process

During the gradual uplifting of the Colorado Plateau, starting about 60 million years ago, the still-buried petrified trees were under so much stress that they broke like glass rods. The crystal nature of the quartz created clean fractures, evenly spaced along the tree trunk, giving the appearance today of logs cut with a chainsaw. This process is also explained by Petrified Forest National Park.

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