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Petrified in Beijing (Earthcache)

Hidden : 05/19/2009
2 out of 5
1 out of 5

Size: Size: other (other)

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Geocache Description:

Location and Access

No, this cache is not about Beijing traffic! Here you will find a fine collection of petrified wood from all over China.

Follow the coordinates to the front yard of the Beijing Museum of Natural History located south of Qianmen subway station, west of the Temple of Heaven.

Ignore the signs that say you need to call 5 days ahead for free tickets. Ignore that Lonely Planet says admission is Y15. We found that access is immediate, ticketless and completely free.

Cache can be done 24 hours a day. The information can be gathered from the sidewalk if you can’t get into the grounds.

Earthcaches do not have a physical box or log book. Rather, cachers demonstrate that they learned something from their visit.

To Log this Earthcache:

1. Visit the Site to examine the Petrified Wood (at the coords, on the other side of the washroom building and beside the center steps to the main building).

2. Email the cache owner the answers to these questions:

a) to what useful purposes has some of the petrified wood been put? (two uses)

b) Estimate the height of the tallest Petrified Tree on site.

3. Tell us in your online log something you learned at the site.

Note: This Earthcache site is just outside the Museum of Natural History but since Earthcaches are an outdoor activity, you are not required to go inside. If you don’t go inside you will miss the awesome dinosaur bones, tons of fossils, stuffed animals in native type habitat and many other wonders.

Educational Information:

Petrified wood (from the Greek root "petro" meaning "rock" or "stone", literally "wood turned into stone") is fossil wood. All the organic materials have been replaced with minerals (most often a silicate, such as quartz), while retaining the original structure of the wood. Petrified wood can preserve the original structure of the wood in all its detail, down to the microscopic level. Structures such as tree rings and the various tissues are often easily observed.

When wood becomes quickly buried under sediment and is initially preserved due to a lack of oxygen, petrifaction may occur. Mineral-rich water flowing through the sediment deposits minerals in the plant's cells and as the plant's lignin and cellulose decay away, a stone mould forms in its place. The silicate is attracted to the cellulose, replacing it. Many think that it takes less then 100 years for wood to turn to stone because the process must be completed before the wood rots. However, others claim that the process takes millions of years. For example, the US National Park service has both answers on parts of its website.

However, recent experiments have produced artificial petrified wood in a Washington State lab. In the process small cubes of pine were soaked in an acid bath for two days then in a silica solution for another two. The product was then cooked at 1400 °C in an argon atmosphere for two hours. The result was silicon carbide ceramic which preserved the intricate cell structure of the wood. Soaking in a tungsten solution produced a tungsten carbide petrified wood. This indicates that petrified wood can be formed in a matter of days given the correct conditions (like a volcanic eruption?).

Petrified wood has a Mohs hardness of 7, the same as quartz.

Pure silicate or quartz crystals are colorless, but typically other elements in the water/mud during the petrification process give petrified wood wide color ranges. Collected from various parts of China, the petrified wood samples in Beijing exhibit many colors and are therefore a great place to see the color variety.

Following is a list of contaminating elements and related color hues:

• carbon - black

• cobalt - green/blue

• chromium - green/blue

• copper - green/blue

• iron oxides -red, brown, and yellow

• manganese - pink/orange

• manganese oxides - black/yellow

Additional Hints (Decrypt)

Rnegupnpurf Ebpx!

Decryption Key


(letter above equals below, and vice versa)

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