Colorful rock at the four sisters
Tasks:
- What are the dominant colors visible on the cliff walls near The Four Sisters?
- Based on the color, which mineral(s) do you think are present in the rock?
- Do you notice variations in color intensity? What natural processes might cause these differences?
-
Please take a picture of yourself or an object on site to prove your visit and post it with your log.
Log this cache as “Found it” and send me the answers to the questions to “silka03.earthcache@gmail.com”, my profile e-mail or via Geocaching Message Center. Not in your log!
You may then log immediately. I will contact you if something is wrong.
If there are no answers after 14 days I have to delete your log.
Have fun!
Near The Four Sisters waterfalls, you can see stunning rock walls displaying a range of colors—from beige and orange to deep red and dark purple. These colors are caused by different minerals present in the rock and the natural chemical processes that have altered them over time.
In this EarthCache, you will learn about the minerals responsible for these colors and how environmental factors shape this fascinating geological phenomenon.
The Minerals Behind the Colors
The cliffs in Milford Sound are primarily composed of metamorphic rocks, such as gneiss and schist, which formed under intense pressure and heat. The colors visible today result from specific minerals reacting with their surroundings:
-
Iron Oxides (Hematite, Goethite, and Limonite) → Red, Orange, and Yellow Hues
- These minerals form when iron-bearing rocks are exposed to oxygen and moisture, causing oxidation (similar to rusting).
- Hematite gives a deep red color, while goethite and limonite create yellowish to brownish tones.
-
Manganese Oxides (Pyrolusite and others) → Dark Purple to Black Shades
- Manganese compounds react with oxygen and water, forming dark coatings on the rock.
- These minerals often appear as streaks or thin layers, enhancing the contrast in the rock face.
-
Silica and Feldspar → Beige and White Tones
- Feldspar-rich sections appear light beige or gray.
- Silica-rich areas resist weathering, keeping their lighter color.
How Do These Colors Form?
The vibrant hues of these cliffs are the result of long-term chemical processes, including:
- Oxidation: When iron or manganese minerals in the rock are exposed to air and water, they undergo chemical changes, producing red, orange, and purple tones.
- Hydrothermal Activity: In the past, hot fluids circulated through cracks in the rock, depositing iron and manganese minerals, enriching the rock with color.
- Weathering: Rain, humidity, and natural erosion have further enhanced these mineral transformations, creating the striking color patterns visible today.
https://de.wikipedia.org/wiki/Oxidation
https://www.mineralienatlas.de/lexikon/index.php/Mineral?lang=de
https://de.wikipedia.org/wiki/Eisen(III)-oxid