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Yooperlites at Pebble beach, Marathon, Ontario

This last week, my family and I took a mineral collecting vacation to Thunder Bay, Ontario.  The last stop on the trip was Pebble Beach in Marathon, Ontario in search of yooperlites or ‘glow-in-the-dark’ rocks are the locals know them.

The yooperlites is the name these rocks have in upper peninsula of Michigan, along the southern shore of Lake Superior.  I purchased on for reference.  The specimen is a very common looking gray and white mottled igneous rock containing fluorescent sodalite.

So, I started doing some research (using my software Digital Rockhound’s companion) and found areas where syenite (silica deficient rock composed mainly of alkali feldspar and ferromagnesian minerals such as hornblende and in certain locations sodalite.  Famous area is Bancroft, Ontario (much further east) where sodalite has been mined.  I was looking for a source closer to Lake Superior and the Upper Peninsula of Michigan.  In the images below, the red is syenite and there is a large deposit located in city of Marathon.  

These images were created in DRC 4.0 (not released yet August 2019!) using geology of Ontario shapefile from the Ontario Ministry of Mining, Bing aerial view in Mapsui for WPF.
Researching Marathon, I discovered Pebble Beach, which could be renamed cobble or boulder beach.
Some images from Pebble beach:

I purchased 6 high powered long wave ultraviolet lights from  A word of caution, these flashlights are 100 UV LED light source that is very bright.  Some people are sensitive to blue-purple frequency light.  I know in indoors using one of these flashlights on my mineral collection I get a head-ache after about 15 mins of use but outdoors these are fine.  You can spot a strongly fluorescent mineral at 3-4 feet away.
My family scanning about 1 km of beach with the lights.

In the end, we found about 8 fluorescent stones, 3 very nice ones and 4 larger cobbles with single fluorescent crystals, and one odd stone fluoresces pale red (still researching this one).
Here are two of the nicer stones.

(Updated) A nicer photo with truer color.  Used my trusty 40 year old Raytech UV light.
Things to know before you go…
  • During bug season, you will need bug spray.  Gnats, mosquitoes, and black flies were very  thick the evening we were on the beach.
  • Pebble Beach is a local park and is well marked with parking and playground nearby.
  • It is a steep walk down to the beach and the beach itself is difficult, high ankle hiking boots are recommended.
  • Go to the beach before sunset to get the lay of the land before exploring the beach after sunset.
View of Lake Superior at Marathon.

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