Category Archives: Michigan Stones

Thomsonite and Prehnite

Rockhounding the the Keweenaw Peninsula of Michigan is one of my summer highlights. A distinctive set of stones are found there, many related to the presence of native copper. In this article I would like to talk about thomsonite and prehnite which are different stones, but sometime share the same name.

True Thomsonite may occur in the Keweenaw Peninsula of Michigan, but is generally not associated with copper.

Thomsonite is a zeolite akin to minerals such as tanzanite. pb2303101Thomsonite is a lovely pink stone sometimes featuring “eyes” and chatoyant sprays. The very best has always been associated with a small area near Grand Marais, Minnesota along the north shore of Lake Superior. The collecting area in that location has been closed to the public for many years, but Thomsonite pebbles still roll up on the beach near Grand Marais. The difficulty lies in most of the beachfront property being private property.

thomsonite

Most of what we use to refer to as Thomsonite from the Upper Peninsula is really copper-bearing Prehnite, or what is sometimes referred to as Patricianite. If you find what you believe to be Thomsonite and it contains specks of copper, it probably is Prehnite. The inclusions in the Prehnite are endless and create lovely pastel colors. Often “eyes” are present as are variegated type feathery patterns. We refer to these gemstones on our website as U.P. Thomsonite (this is what the locals call them also).

U.P. Thomsonite, in my opinion, is the most remarkable gemstone found in the Keweenaw. The striking chatoyancy and pastel colorations of this stone are something to behold. It is impossible to photograph the chatoyancy of true Thomsonite and U.P. Thomsonite as you really need to move the stones back and forth to see this effect. Thomsonite is much more expensive and scarce than Prehnite, but many people find the U.P. Thomsonite more attractive.

p9060246 Good, jewelry-grade Patricianite is still hard to come by. It took me ten years to locate a spot to dig this wonderful stone. The locals will not easily give up their best rock hunting locations, so you may be on your own when it comes to finding U.P. Thomsonite.

Our website features some of the finest Thomsonite and U.P. Thomsonite available.

Native Copper

The largest and greatest deposits of native copper ever discovered occur in Michigan’s Keweenaw Peninsula. These copper deposits have been exploited since prehistoric Native Americans used hand tools made of rocks to chisel out the almost pure copper from exposed surface areas.

Native copper is very rare throughout the world. Copper deposits are not ordinarily comprised of large masses of almost pure copper. The copper from the Keweenaw is most often “polluted” with silver, making it even more conducive to electrical uses.copper

The habits of copper growth are too numerous to list, but one of the most coveted by Keweenaw-area collectors are silver and copper combinations known as “half-breeds”. Beautiful crystal copper formations are also sought, as are copper-included minerals such as Datolite, Prehnite, and Greenstone.

The history of the Copper Country is interesting to study and many wonderful books have been written on the subject.

We sell native copper, both cleaned and raw, as well as special pieces like the aforementioned half-breeds. We also have raw chunks of copper that have been through the hammer mills and most likely carried off by miners in their lunch pails. Another interesting throwback to the copper days is Firebrick, almost impossible to find now. Bricks lined the smelter walls and over time became permeated with molten copper. After the mines closed, some of this material was rescued when the smelters were closed, back in the 1960’s.

Currently no producing mines are left open in the Keweenaw, the tunnels are flooded, and the discard piles are gradually being crushed for road gravel. I have seen collecting opportunities in the Keweenaw declining rapidly over the past 20 years as old mine discard piles disappear, and collecting areas revert to private property. Much of the gemstone material I used to collect is now impossible to obtain in the field. Now is the best time to invest in jewelry and specimens from the Copper Country while the prices are still affordable.

A few mines are still open for tours: the Delaware Mine between Calumet and Copper Harbor, the Adventure Mine near Ontonagon, and the Caledonia Mine, also near Ontonagon. The Caledonia Mine offers collecting opportunities both underground and on the surface by appointment. Specimen collecting is still underway by the owner of the Caledonia, Rich Whiteman and his crew.

We offer the very best jewelry manufactured from rare copper country gemstones. Many of the materials we use are purchased from collectors in the area or found by us in our rockhounding forays to the area each year. Our beaded bracelets combine many U.P. stones including agates, epidote, and kona dolomite as well as the copper-related stones. Our Datolites sometimes have great bits of copper in them–Copper Datolite with Epidote, and Datolite, Copper Lightning. We use only the finest quality rough materials to create our finished products, and truly believe our U.P. jewelry line is the finest anywhere.

Ghostbusters

“Ghostbusters” is another pendant of the “Debbie Collection”, one of her earlier purchases. When Halloween time comes around, you often see her showing off how her ghost seems to fly through the air!

My inspiration on this one came as I was cutting slabs from a very unusual Lake Superior Agate. The agate had distinctive eyes as well as some fortification structure with unusual coloration, mostly white but including some yellow, which is quite rare in Lakers. I immediately saw a face on the second slab, and the pattern continued through the next three slices.

I cut a calibrated oval 30X40 mm cab with the eyes in a position showing the face of the ghost. The position of the eyes toward the side of the cab made me think of a flying ghost.

I took this cab to William Holland School of Lapidary Arts in Young Harris, Georgia for an advanced wire wrapping class I was taking. The first incarnation of the ghost came into being at that time. I thought the piece was quite whimsical and artsy. I kept that piece of jewelry around for a couple of years and my wife wore it at Halloween time each year. Debbie was looking through my pendants one day and fell in love with the ghost. By the time she looked at the original piece I had made a second, less extravagant ghost pendant, but Debbie wanted the wild unit I had created at lapidary school. p12600032 I re-wrapped the original ghost simply because my skill level had progressed substantially and I could see some flashier things to do! This is the pendant that Debbie loves.

The ghost appears to be flying rapidly through the air throwing up a trail of smoke. I really enjoyed creating this extra-ordinary apparition.

Datolite Jewelry

Datolite is a mineral closely associated with the copper mines in Michigan’s Keweenaw Peninsula. The natural coloration of Datolite is white, but I have seen or collected Datolite in gray, green, pink hues, mauve, brown, red, orange, black, and the most rare, yellow. Any combination of these colors is possible. Small specks of copper and other inclusions may be present.

Datolite nodules, rough and cut

Datolite nodules, rough and cut

One of the things that make Keweenaw Datolite unique is its nodular form. Nodules are difficult to locate on a rock pile, because they blend into the background rock. A small glint of color or a rounded cauliflower shape might be the only clue that this valuable gemstone is hiding right in front of your eyes. Crystals of Datolite also occur, but to a lesser extent than the nodules. Datolite also can form in seams.

Datolite makes wonderful and colorful jewelry, and our Datolites represent many mines in the Keweenaw. I hunt Datolite as well as purchase specimens found by others to produce my jewelry. Datolite from the Keweenaw, as well as other minerals, is becoming scarce due to several factors including the mine dumps being on private property, or being ground up and hauled away for road fill. I have seen a steady price increase in Datolite in the past few years as the sources vanish. Now would be a good time to invest in these beautiful and rare gems!

Greenstone and Datolite have been designated as Michigan’s only true precious gemstones. Quality wire-wrapped Datolite jewelry is my specialty. If you have a special request for Datolite contact me.

For even more on the colors of Datolite found in each mine, click on this link to Jeff Anderson’s web site Dwarves’ Earth Treasures.