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Cat Rocks on Little Kinmen 小金門的貓公石 EarthCache

Hidden : 05/06/2019
1.5 out of 5
1.5 out of 5

Size: Size:   other (other)

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Geocache Description:

This Earth Cache introduces the geologically interesting and unique Cat Rocks, located on the north coast of Little Kinmen Island. This is the only area of Taiwan where this type of stone can be found.

To log this cache you will need to visit the Cat Rocks area, make observations, and then answer task questions based on your observations and from the information below. You should not have to research any further. I've tried to make the information as non-technical as possible.

What gives rocks their colors?

Basic elements found in minerals help give them color. These colors can be affected by a number of factors including light, heat, radiation, and impurities.

Below is a list of some elements and the colors they often produce in minerals:

  • Cobalt: Violet-Red
  • Chromium: Orange-Red
  • Copper: Blue
  • Iron: Red-Brown
  • Manganese: Pink-Purple
  • Nickel: Green
  • Uranium: Yellow

Task 1: Observe the Cat Rocks along the shoreline, at the base of the cliff walls. Based on the predominate color you see in the rocks, which element appears to be in abundance?

How are rocks formed?

Rocks are made by three methods:

  1. Melted and cooled: When volcanic lava cools, whether inside the earth or when it flows to the surface, it becomes solid and forms igneous rock.
  2. Cemented together: When rock fragments, seashells, and chemicals combine with the action of water, they become solid and make sedimentary rock.
  3. Squeezed and heated together: When extreme heat and pressure bake rocks, their structure can completely change and become metamorphic rock.

Task 2: Cat Rocks come from the surrounding cliffs. These cliffs are composed of various layers of soil and rock. The Cat Rocks were formed when the element referred to in Task 1 was leached from the upper soil layer and moved by water to bond with pieces of clay, quartz, sandstone, and limestone from the layers below. Based on this information, what kind of rock are the Cat Rocks?

Basic Erosion

The unique features of the Cat Rocks are a result of erosion. Erosion is an action on the surface of the earth (like water movement) that removes rock, soil, and dissolved materials from one location and moves them to another location. These processes are often categorized by the following causes:

  • Water
  • Snow and Ice (glacial)
  • Wind (aeolic)
  • Chemical (corrosion)
  • Gravity (mass movement)
  • Plants and Animals (zoogenic)
  • Humans (anthropogenic)

Coastal Erosion

Coastlines, like the Cat Rock area, are especially vulnerable to erosion. This occurs due to the combined actions of ocean waves and tides, estuaries, storm impacts, chemical processes, and other natural and unnatural forces. Some of these forces are:


This happens when waves break on a cliff face and erode it. The water itself slowly wears down the cliff, while also slamming rock fragments against it, causing yet more erosion.

Hydraulic Action:

When ocean waves strike a cliff face, the force from the water compresses air inside cracks in the cliff. The resulting air pressure causes the cracks to grow and rocks to splinter. The splintered rock can add to the erosion process (attrition).


Attrition occurs when waves cause loose pieces of rock debris to collide with each other. They grind and chip each other, progressively becoming smaller, smoother and rounder. This is similar to sandblasting or using sandpaper.


Corrosion, also known as solution or chemical erosion, takes place when the sea's salt, acids, and other chemicals dissolve some types of rocks, especially those with higher pH levels like chalk and limestone. Wave action increases the rate of erosion by removing the dissolved material.

Task 3: Observe the the surface of the Cat Rocks, as well as the area around them. Take into account the materials that the rocks are made of as described in Task 2, as well as this location. Which coastal erosion process do you think was responsible for their unique surface, and why?

Task 4: The name of these rocks in Mandarin Chinese is 貓公石 ("cat stone"), but it actually comes from Taiwanese Minnan slang, describing a man's face. Based on your observation of the Cat Rocks' surface, what does this slang term mean?

  1. "Bearded Face" (stubble surface)
  2. "Baby Skin Face" (smooth surface)
  3. "Pimple Face" (bumpy surface)
  4. "Pockmarked Face" (cratered surface)

Task 5: Feel the Cat Rocks. Now, pick up some sand at your feet. Examine and feel the sand. Compare the Cat Rocks and the sand and answer the following questions:

  • Is the color of the sand more similar to or more different from the color of the Cat Rocks?
  • How is the texture of the Cat Rocks different from the texture of the sand?
  • What erosion process(es) do you think contributed to the difference in textures, and why?

You may log your find as soon as you send me your answers, but you must visit the site and complete the tasks. I hope you enjoy your visit to the Cat Rock area of Little Kinmen!

Additional Hints (No hints available.)