By Jeremy Zolan – follow him on Instagram Leaverite_Tycoon
Overview: Specimens of smoky quartz forming in granite are commonly seen from Colorado, California, Montana, or New Hampshire and not associated with Wisconsin! Surprisingly, there have been quite a few nice specimens of smoky quartz and feldspar found in Wausau County, approximately around the Rib Mountain area. Known mostly among locals, this area hasn’t gained much popularity among collectors, but has the potential for many future great finds.
Smoky quartz from the Nine Mile Pluton in Wausau County, Wisconsin. 9cm field of view! Photo by Al Falster : https://wgnhs.wisc.edu/minerals/quartz/
A beautiful, gemmy beryl from the Nine Mile Pluton in Wausau County, Wisconsin. Tiny crystal. 2cm field of view. https://wgnhs.wisc.edu/minerals/beryl/
Prospecting: Even though most of the locations that yielded the specimens above are likely private, there are probably plenty of other areas one could find to dig crystals since specimens are recorded as coming from a variety of spots within the area. See Mindat for more info: https://www.mindat.org/loc-24286.html
Localities in Marathon County recorded to mindat.org
Viewing the image above, one can see there is a huge amount of localities in this area. Looking at the mineral list and description on Mindat, the location is known for extremely old rocks and nice exposures of them- “ Marathon County displays some of the best outcrops of Precambrian rock in the state. Many of the rock occurrences are of interest to the mineral enthusiast.”
Many of the ancient intrusions that blasted through the complex igneous and metamorphic country rock are of unusual compositions. Additionally, they are extremely weathered and “rotten” meaning they are very easy to dig through.
Granite when unweathered tends to be one of the most difficult rocks to work, and hard rock mining it is a laborious task. Due to the fact that that the granite has been decomposed to the point where it falls apart means no hammer or chisel would be needed to dig them. Perhaps just a shovel or pickaxe!
Notice how this granite is just falling apart into pebbles. At this particulat quarry, the Beilke Quarry, a variety of minerals were found including Microcline, Smoky Quartz, and Phenakite. This location is private and reclaimed.
It seems like the rotten granite occurs around Wausau. I would try to find some sort of public land you could freely prospect, or contact someone with interesting rotten granite or an abandoned quarry on their land. Crystals may be loose in the dirt, or may be clustered up and held together with clay within the weathered granite. Minerals found in the boulders are also reported. Weathering and alteration often left “cores” of more resistant rock.
This granite is “miarolitic” meaning as it rose when it was injected into the continent, gases dissolved within it bubbled out as it depressurized. These bubbles often were trapped in the solidifying rock before they could diffuse, and crystals grew inside as the rock cooled and vapors interacted with quartz, feldspars, and micas.
The premier location in the area appears to be the Bielke Quarry in Wausau, which unfortunately is reclaimed and off limits, but yielded beautiful specimens of amazonite that are of notable quality for the US. See: https://www.mindat.org/gallery.php?loc=24286&min=2704
Rib Mountain, contained within Rib Mountain State Park may be a good area to start learning about the local geology. Mineral collecting is likely not allowed in the park, but one could look around for crystals to understand the geology, but leave them be. Crystals have been reported as coming from Rib Mountain, so searching for pockets in granitic rocks exposed there may be a good place to understanding how to find them where you could regularly dig for them.
Searching around, I found a local talk about finding a large pocket of fine smoky quartz in his back yard. Props to this guy for having some nice collecting he can do so easily!
As you can see, a gorgeous smoky. Check his other Wisconsin minerals out here! http://huntforgems.com/minerals/wi.html
He states he found 32 crystals so far and they were embedded in a red clay. Interesting to note what he found them in.
Tools: Unlike some miarolitic granites which are very hard, these Wisconsin granites are often weathered to the point where you would expect to use a shovel, pickaxe, or hoe to move material. Use a screwdriver, chopstick, or bamboo skewer as a probe when you see anything that looks like a pocket. Wooden pocket tools are the safest for removing the crystals undamaged.
Unweathered granite is present in Marathon County too, and this can be mineralized. For this kind of rock, crack hammers, chisels, wedges, and prybars are likely your tools of choice.
There are a diverse array of minerals in this area of Wisconsin, so you will need to be creative and adaptable.
Conclusion: Considering the abundance of specimens of Smoky Quartz and Feldspar from Colorado, other locations with the same kinds of minerals are frequently overlooked. This example of such an overlooked area with similar mineralization deserves more attention, as it seems to be slipping into obscurity. This article serves as a guide to get the mental juices flowing, to help perhaps inspire a collector to make an exciting, beautiful find in this area.