Rainbow Cave, Pictured Rocks National Lakeshsore, MI

AlanLichty

Moderator
Wow - didn't know this existed before now. Interesting hues that include a lot of blue. What mineral is contributing to that?
 
Wow - didn't know this existed before now. Interesting hues that include a lot of blue. What mineral is contributing to that?
The blues and greens are formed from copper carbonates (azurite is blue and malachite is green). The reds and yellows are from iron oxides (hematite is red and limonite is yellow). Green can also come from reduced iron oxides. I didn't very close to this in order to tell but I suspect that some of the green is due to algae and small plants.
 
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AlanLichty

Moderator
The blues and greens are formed from copper carbonates (azurite is blue and malachite is green). The reds and yellows are from iron oxides (hematite is red and limonite is yellow). Green can also come from reduced iron oxides.
Thanks - I didn't know the area around the lakes had copper deposits.

I did my masters thesis on pigments used for frescos in Petra and the color blue was very hard to come by circa 100AD. Most of the easily mined azurite was gone so they were using blue frit (Egyptian Blue) also known as artificial copper calcium silicate.
 
Thanks for providing the neat information about copper pigments, Alan. There were actually minable deposits of native copper on the Keweenaw Peninsula which was the copper mining capital of the world at one time. So I am not surprised that there are secondary deposits at Pictured Rocks National Lakeshore.
 

JimFox

Moderator
Staff member
Very interesting Doug! I was too young when I lived in Minnesota to explore places like this, but I sure would like to some day.
 
Very interesting Doug! I was too young when I lived in Minnesota to explore places like this, but I sure would like to some day.
It is different kind of beautiful from what we see here in the west. I would love to show you around. It might be neat or organize a trip sometime with all of the folks from the west. I'll show you some other great spots too in the near future.
 

AlanLichty

Moderator
It is different kind of beautiful from what we see here in the west. I would love to show you around. It might be neat or organize a trip sometime with all of the folks from the west. I'll show you some other great spots too in the near future.
Fun thought - I have spent most of my life on the west side of the Rockies. My personal experience for everything east of there consists of flying over it going somewhere else.
 
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