Pillow Basalt EarthCache
Hidden : 1/6/2009
Difficulty:
1 out of 5
Terrain:
1.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:




Pillow Basalt

At this location on Mt. Diablo you will see an example of Pillow Basalt. These pillow basalts formed where two plates of the earth's crust were under water and moving away from each other. Their blobby shape is characteristic of an underwater volcanic eruption, in which the outside of the flow cools and solidifies while the inside is still molten. The presence of volcanic rock on Mount Diablo can be confusing, since the mountain is not a volcano. Though volcanic action created the rock, it didn't create the mountain itself. This rock was forced up by the movement of crustal plates below and around it.

Paleomagnetic and radiometric studies tell us that these pillow basalts formed some 190 million years ago, 3,000 miles out in the Pacific Ocean, below the equator! Pillow basalt is sometimes called greenstone, because the mineral chlorite turns the rock green. However, the iron in basalt gives the rock a rusty tinge as it oxidizes over time.

To log this cache, you will need to complete the following:
- Email the cache owner the (a) Texture of the Pillow Basalt and (b) Estimate the Size of the Pillow Basalt.
- Post a picture of You and your GPS along with the Pillow Basalt.

Parking - Sunset Picnic Area


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