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Two reference books I've found particularly helpful are: Sparky Stensaas' "Rock Picker's Guide to Lake Superior's North Shore" and Susan Robinson's "Is this an Agate." Armed with Sparky's and/or Susan's book plus some of the pictures and descriptions I've provided here, perhaps will help you ID what you are collecting. [Recently I've found another rock pickers reference book that is helping me with agate hunting. It's "Understanding and Finding Agates By the way, if you want to print out any of these larger images, just *right click* on the image and choose "copy image" to copy it to your hard drive. Once there you can click on it and print it out. |
~~~"Click" on smaller images for a larger picture~~~ |
Quartz Quartz is a common mineral found among the beach stones, very hard (will scratch glass), somewhat translucent like frosted glass, and be white to yellow to grayish in color (impurities cause this variety in colors). Generally found as pebbles or imbedded in other rocks. In fact some of the pebbles were formerly amygdules that broke loose from the rock in which they were imbedded.
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Calcite Calcite (calcium carbonate) at first glance may be thought to be quartz as it is a similar color (white to yellowish) and also commonly found, both as pebbles and imbedded within other rocks. But scratch it and you'll see it is much softer than quartz - chalky. To the far right is an amalgam of quartz & calcite > > >
) ) Chert Cherts are a tiny crystal form of quartz. Impurities make them less translucent than quartz. They have a waxy appearance, somewhat shiny. Some of these depicted in the picture "may" be chert. The stone on the far left seems to best meet the description and may be Jasper.
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Flint Flint is a black version of chert. Note the waxy, somewhat shiny surface. ) |
Agate Here's an agate from the display at the Minnesota Geology Center in Moose Lake. Go here to see more examples of agates - both rough and polished.
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 Mystery Rocks Here's a few that I have yet to narrow down. You can't see it in the photo, but rock A has tiny flecks of sparkly crystals throughout. Rock G. might be Jasper? Rock N has a texture somewhat like sandstone but it seems too solid, heavier than the sandstone I know. Likewise Rocks C & H appear to have sedimentary layers as if they were sandstone or limestone, yet again each has a more solid rock feel/hardness that I don't associate with sedimentary rocks. Rock K. may be slate, yet it is more rounded and pebble shaped than what I gather you'd find in slate. If Rock M was solid, I'd guess Jasper but I haven't found in my reading that quartz veins can be imbedded within Jasper as they do in this sample. Further reading and inspection have caused me to question if the greenish stones labeled "epidote" are correct? If you have an idea on any of these mystery samples, please drop me a line. roscoetrails@gmail.com
And also if you disagree with some of the rocks I have labeled, please speak up!
Reference Books Stensas, Mark Sparky and Kollath, Rick, Rock Picker's Guide to Lake Superior's North Shore, Duluth, MN: Kollath-Stensas Publishing, 2000. Robinson, Susan, Is this an Agate - An Illustrated Guide to Lake Superior's Beach Stones in Michigan. Hancock, MI: 2001
"Agates: Treasures of the Earth
Links for Rock Picking on Lake Superior Beachs and information on Agates and Rocks found around Lake Superior
For a nice introduction to rock tumbling, see Cheralyn Maturi's Minnesota Iron Range Website |
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" by Karen Brzys. )
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." Roger Pabian, et. al. 
