Tag Archives: Prehnite

Patricianite (or not!)

Apple Green Prehnite appears as vein material in some mine spoil piles from Calumet north. Normally it has fine Native Copper inclusions. This is some of the “Chunky” variety of Prehnite mixes. Notice that this material forms in veins, as does Patricianite, in most cases.

Before I can address how to identify Patricianite, I have to address the main ingredient–Prehnite. Prehnite occurs generally in vein material in many of the mine waste piles in the central Keweenaw Peninsula area from Calumet north to Copper Harbor. Prehnite is formed in veins and cavities in Keweenaw basalts, and is associated with other Keweenaw Minerals, including Calcite, Datolite, Chlorastrolite (Greenstone), Quartz, and Zeolites. It is also closely associated with Native Copper.

Typical Prehnite Mixes and Patricianite Beach Pebbles. These pebbles often have Copper inclusions and beautiful radiating eyes, similar to Thomsonite, hence the local name of U.P.Thomsonite is commonly mentioned.

Patricianite and Prehnite, from the Keweenaw Peninsula, come in both smooth or chunky, just like peanut butter. Smooth beach pebbles of White, Pink, and Green are not uncommon finds in the Keweenaw, The pastel colors often appear stirred together. Chunky Prehnite or Patricianite are found in the mine spoil piles, roads, or secret holes near Thomsonite Hill. The forest roads sometimes produce nice Prehnite mixes. Here’s a secret; some of the Prehnites appear white, and is often passed over on these forest roads. The colors and patterns are hidden under this thin rind and are not visable until this rind is removed.

Patricianite is a special variety of Prehnite, named by Rosendahl, in 1966, after his daughter Patricia Ann. Green Prehnite with inclusions is not considered Patricianite. In order to have Patricianite, you must three ingredients: 1. Pink Prehnite; 2. Chlorite; and 3. Visable Copper Inclusions. If any of these three elements are not visable, you do not have patricianite. (pink prehnite is light apple green prehnite containing microscopic specks of copper that have changed the green Prehnite to pink shades). The more Copper in the mix, the darker pink; I have found a few Prehnite pieces that are actually Maroon from so much Copper. If you hold these pieces in the sunlight the massive ammount of micro-copper is very evident.

I usually like to write a new blog and have it published close to the first of the month. I wanted to write about Patricianite, but I could not find a good piece anywhere. If you have so many rocks, you can’t find A rock, perhaps you have too many rocks; NOT! While searching for a nice piece of Patricianite, lo and behold, I discovered some amazing Datolite. Now I’ve become distracted by the Datolite I forgot I had. While looking through the old Datolite, I found a small slab of PATRICIANITE. At a glance, Patricianite can look like Datolite, that’s why it was there. So amazing things lost years ago (can something be lost, it you don’t know it’s lost?), were found today. Now, even though Greenstone is being worked in the shop, the Datolite is calling.

The pebbles of Prehnite found on the beaches, are generally a combination of beautiful apple green, pink, white, and other colors which appear stored together (smooth), while the mine spoil piles produce chunky seam Prehnite. Usually the seams aren’t much more then an inch wide, and if you are lucky, you can find gem green Prehnite visibly peppered with copper. Prehnite in these seams seems to form from both sides of the seams, and either meets in the middle of the seam, or there may be a gap right down the middle of the seam. Bubbly, boitrioidal, Prehnite is also found on the spoil piles. This Prehnite is translucent and has a vitreous luster. If you find one of these, you have a great specimen.

There was so much Copper in this Prehnite that the stone was Maroon. Patricianite?; Some call this Patricianite, but not the classic mix.

Prehnite with copper and Chlorite. No Pink, so this isnot Patricianite.

A beautiful pink and white Prehnite cab, but no evidence of Chlorite. Copper IS in there, but I can see no Chlorite.

A close-up of the previous cab, reveals visible Copper, but I see no Chlorite. I believe this is Patricianite, but I would not argue the point. That Chlorite has to be in there, doesn’t it? Under magnification that triangle in there looks loke a Pseudomorph of Aragonite, doesn’t it?

Copper and Patricianite mix, but green so Not Patricianite.

This is Patricianite; all the right ingredients and more.

Prehnite in the Keweenaw is sometimes referred to as UP Thomsonite. People used to think Prehnite was a form of Thomsonite until testing by Michigan Tech proved that it was not. Prehnite can have eyes, and radiating crystals similar to Thomsonite, but Prehnite is not a Zeolite, as is Thomsonite. TRIVIA: Prehnite is the first modern mineral named after a person. You can read about this on one of my previous blogs. https://www.snobappealjewelry.com/blog/can-you-make-jewelry-from-keweenaw-prehnite/

Prehnite is a favorite stone to make Keweenaw Stone Jewelry from, the shiny copper bits and pink and green color variations make it interesting and popular. High quality, gemmy Patricianite and Prehnite are highly prized for jewelry and collecting. Visit our Prehnite Jewelry page.

See other jewelry from Keweenaw rocks and minerals: Greenstone, Datolite, Firebrick, Mohawkite, Thomsonite, Lake Superior Agates.

Just as an aside; In order to do the research for this article I happily dug into my collection of old Rock & Mineral books. Every time I do this, I pick up little known and forgotten facts. I was reading “Rocks and Mineral of Michigan” published by the State of Michigan Department of Conservation (now the Department of Natural Resources; DNR) in 1939. It was so old it referred to MSU as Michigan State College, and MTU as Michigan College of Mining and Technology. I’ve got to re-read this book and perhaps find a new rock hunting area lost in the past.

Prehnite and Other Pebbles from the Keweenaw

I discovered quite a few samples of Prehnite mixes that I found in the Keweenaw. All of these came from my cabochon collection, so I decided, this month, to follow up my blog on Patricianite in October, by showing you a small sample of what can be found on the beaches and in the hills of the Michigan’s Keweenaw Peninsula. Out of all the rocks and minerals in the Keweenaw, these little Prehnites are one of the most common treasures. On the beaches they wash in as pastel pebbles standing out against a rocky background of reds and browns. In the forest roads, quite often, Prehite’s have a white crust ( a little secret Rockhounding tip) with no clue as to what is hidden under the crust. I just pick them, take them home, and grind off a bit of crust. Maybe there’s treasure under the crust, maybe not.

I do not own expensive scientific instruments like a Scanning Electron Microscope (SEM), so I do not have the capability of analyzing every Prehnite mix I find, but I can tell you there is no limit to Nature’s recipes in regard to these beautiful pastel Treasures.

You may know that in the past, because of their resemblance to the Zeolite Thomsonite, this variegated, sometimes eyed Prehnites, were thought to be Thomsonite. Research done at Michigan Tech revealed that these “U.P. Thomsonites” were substantially Prehnite Mixtures. The old time rockhounds still refer to these as U.P. Thomsonite.

Sometimes you feel like an eye, sometimes you don’t. I suspect the suspect on the left may include Datolite.

Lovely pastel greens and pinks (color caused by micro-copper inclusions) dominate U.P. Thomsonite.

The patterns are so varied it's amazing.

The patterns are so varied–collecting is fun and addicting!.

Notice the brachiation (various spellings) in the right hand stone.

Jewelry grade

Can you make jewelry from Keweenaw Prehnite?

Botrioidal Keweenaw Prehnite rough

A thin Patricianite seam. Yes, that copper sheet is embedded in it.

Patricianite Rough (Non-seam material)

Here’s a little trivia you may not know about the mineral Prehnite: The first modern mineral to be named for a person was…..PREHNITE. Abraham Gottlob Werner of the Freiberg Mining Academy, was a popular teacher, but is also credited for delaying the advance of Geology by insisting upon wrong concepts on the origin of rocks and minerals. He WAS successful in classifying minerals. Werner named the mineral Prehnite after Col. von Prehn after von Prehn brought the mineral to Europe from the Cape of Good Hope (1783), where he found it.

I love rock trivia. I found this knowledge in a 45 year old book I have. Let’s take a look at some of the variations of Keweenaw Prehnite. Where possible I will show the cabochon before it became jewelry.

This Patricianite sports loads of Copper. I think it would look good as jewelry.

Why, yes indeed it did look good as jewelry.

Prehnite is a Copper Associate Mineral in Copper Country. Much of the Prehnite contains copper dust that changes green Prehnite to pink Prehnite. Other inclusions in Prehnite also produce a plethora of colors. Zeolites sometimes mix with Prehnite (A calcium Aluminum Silicate) in the Keweenaw and produce feathery eyes and patterns. Copper and Chlorite included Prehnite is sometimes referred to as “Patricianite” by copper country locals.

Pastel Patricianite with small Copper Inclusions. This was a massive chunk before slabbing.

Another one that made great jewelry.

Pastel Prehnites roll up on the beaches all along the west side of the Keweenaw Peninsula. While looking for agates, beachcombers may see a bright pink stone shimmering among other dull stones. Pick it up, it might be a coppery beauty. These nuggets can have pink and green together, sometimes even purple tones. I have found Prehnite in piles of materials cleared from road construction not far from Calumet. Prehnites are also gleaned from rock spoil piles at some mines. I have a secret hole that I also occasionally excavate for Prehnites. The best Prehnite has always been associated with Austraiia, but gemmy pastel green Keweenaw Prehnite with Copper inclusions, in my opinion, gives the Aussie stuff a run for the money.

Prehnite with Copper. This is the high quality stuff often found in slim seams.

Prehnite with very little Copper. This is the high quality stuff often found in slim seams.

Prehnite is sometimes referred to as U.P. Thomsonite because its’ appearance often mimics Thomsonite, with eyes, radiating sprays, and variegated inclusions. Some Prehnite is difficult to tell from Thomsonite, or other Zeolites, and for many years Prehnite was thought to be a Zeolite. It was determined by Analysis by Michigan Tech geologists that Prehnite is not related to the Zeolites, but can be associated with Zeolites. Prehnite is a Calcium Alumosilicate. More confusing is when Zeoiles mix with Prehnite and make the Prehnite look exactly like Thomsonite. Thomsonte is almost an exclusive American Gemstone (more trivia for you guys), Prehnite is much more scattered and can be found in numerous locales around the world.

Loads of Copper in this Prehnite. Mine seam material.

Loads of Copper runs through this Prehnite, a mine seam material.

A beautiful oddball dug from a hole somewhere in the Keweenaw Peninsula. Prehnite, assorted Zeolite and other stuff. A beautiful mix, don’t you think?

The Apple Green Prehnite from the Keweenaw can be found as small round Crystals, but in most cases as slim veins in the Amydaloidal basalt. I have found much of the Prehnite in my collection in veins that are less that one inch. The Prehnite seems to form within a void from the outside in, meeting in the middle of the void. After extracting the Prenite bearing host basalt, I usually split the Prehnite where it meets in the middle. I can then use both sides to make beautify cabochons and jewelry. I like when the Prehnite sometimes does not completely close off in the middle of the seam, leaving a void where Prehnite Crystals form in a drusy. Remember it is often possible to find copper within the U.P. Prehnite. Copper can be found included in most every Keweenaw mineral.

The Seaman Mineral Museum, in Houghton, Michigan, has some wonderful, large Prehnite crystals found by miners over the years. Knowing that a Mine Captain or Superintendant or other mine management person was a mineral collector, the miners could score some points by turning these specimens over to them. Some of the finest specimens at the Seaman Museum were from these historic collections donated to the museum by heirs or willed by the owners of the collections.. Two of the most prolific collectors were J.T. Reeder, who clerked at several different mines, and L.L. Hubbard who discovered the Champion Mine and served as general manager of the mine. It is interesting to read and learn about these early collectors. Hubbard willed some of his collection to the University of Michigan, and recently the U of M has given many Copper Country specimens, from historic collections, to the Seaman Museum.

Many rockhounds overlook Prehnite or Patricianite while rock collecting in the Keweenaw. it’s one of my favorites and I never miss a chance to pick up nice pieces. So what do you think? Does Prehnite/Patricianite make good jewelry? You are invited to visit my jewelry pages to see the variety created from Keweenaw Treasures, especially Prehnite .

Canadian Rocks and Jewelry

Michipicoten Agate with Amethyst. A rare Lake Superior Agate, I call this Samethyst because of the salmon color and amethyst center.

I met my new good friend John when he called me based on seeing my Snob Appeal Jewelry website. John said he had acquired an old collection of Canadian rocks and minerals. I was immediately interested when he described some of his treasures, including a quantity of Michipicoten Island Agates that were removed over 70 years ago.

Michipicoten Agate with Moss.

John's wife loved this pretty pink picture in this Michipicoten. What an unusual Lake Superior Agate pendant!

Michipicoten Island is now a Provincial Park, but 70 years ago it was not. Provincial Parks in Canada are the equivalent to National Parks in the U.S., and are protected. Collecting rocks today can get you in big legal trouble. The Michipicoten Agates are not rare on the island, but cannot be taken.

Michipicoten Agates formed in very fluid basalt and are an oval shape, rather than round, and formed in pockets. Like other Lake Superior Agates, they are varied in colors and types, coming in all sizes, types, and colors. Some that are not this oval shape look more like carrots, and are locally referred to as “Carrot Agates”. Some will make great jewelry, and some are better as specimens.

I am still trying to figure out what exactly this Green Mystery Rock is called.

Although I don’t live far from Canada, I am not very familiar with Canada’s rock and minerals. Additionally some of the material I’m running across was collected over 50 years ago. These older pieces often are from played out locations. Sometimes a familiar rock looks quite different from the specimens that can be seen today.

The Mystery rock sure makes spectacular jewelry.

One of these special Canadian rocks is beautiful green with Amphibole type (needle-like) crystallization. I sliced the rock into slabs and put it up on a Lapidary Facebook Group I belong to. Many guesses were made, but this rock seems to be a combination of minerals. I suspect it is a Chlorite with Quartz. I am taking the mystery green rock to the Seaman Mineral Museum to see if I can get a better identification.

Another interesting rock was a Rhodonite that had flowing pastel blues throughout it. You can certainly find Rhodonite today, but I usually see it with black inclusions, not pastel blue!

Pastel colors abound in this Rhodonite.

I expect this is Prehnite with Copper Inclusions is similar to the Patricianite we find in the Keweenaw.

John also had a copper-included rock similar to the Patricianite found in the Keweenaw, but not as pretty as the Keweenaw material. I had not seen the copper-included rocks in Canada, so this was interesting to me.

I found flower type formations in Calcite, as well as other, what I suspect, is Prehnite flowers in another rock. These are pretty and intriguing. I can’t keep my saws and grinders going fast enough!

I suspect these are Prehnite Flowers.

These flowers are in Calcite. I have not figured out what these red, Canadian, included material is.

John and I hit is off, so I expect I will go rock hunting with him next spring. I’m looking forward to finding new and unusual rocks in the Canadian wilds.

Cliff Mine-Prehnite Hunting

The hounds are released on the Cliff Mine Pile.

The pile was bulldozed and the Copper Country Mineral Retreat hunt at the Cliff Mine began at 9am. A good crowd of eager hunters attacked the pile. A nice trench was excavated and some entered it while others, like me hunted the surface. The Cliff, even though hunted for over a hundred years by rockhounds, still produces some fine copper specimens as well as other copper associated minerals. Native American Indians hammered this copper in prehistoric times, and chisel chips left from their mining are found at the Cliff today.

A nice trench was excavated and our buddy Keith from Baltimore found his way into it.

A great view of the Cliff mine showing the trench that fellow rockhounds were searching.

Since I already have so much native copper, Bonnie and I spent the day hunting for gem Prehnite for our jewelry. The Prehnite at the Cliff formed in small veins maybe a few inches thick and is apple green and speckled with copper. We were quite successful and found good pieces with some help from Pam Hecht who is a good buddy and led the hunt.

Prehnite comes in various forms and colors in the Copper Country. One of my favorites is referred to as “U.P. Thomsonite” and is verigated, often with eyes. Prehnite comes in assorted pastel colors, the most common being pink and green.

A seam of Copper bearing Prehnite from the Cliff Mine.

Here is some of that Prehnite on my workbench. Notice the copper?

The Cliff mine was the first successful copper mine in the Copper Country of the state of Michigan. The mine is at the now-abandoned town of Clifton in Keweenaw County. Mining began in 1845, and the Cliff was the most productive copper mine in the United States from 1845 through 1854. Large-scale mining stopped in 1878. The Cliff was a fissure mine where the seams of copper were vertical.

Fissure mines are always interesting to search. I spent the day looking for gem quality Prehnite, and Bonnie and I found many nice pieces. These veins of Prehnite are commonly no more then an inch or so wide with a split down the middle as the Prehnite formed in from the outside of the vein and met in the middle. Much of this Prehnite is loaded with specks of Copper and is a pleasing apple green color.

Although amygdaloid and conglomerate deposits of the Keweenaw tended to be lower-grade than the fissure deposits, they were much larger, and could be mined much more efficiently, with the ore blasted out, hoisted to the surface, and sent to stamp mills located at a different site. Amygdaloid and conglomerate mining turned out to be much more productive and profitable than fissure mining, and the majority of highly successful mines were on amygdaloid or conglomerate lodes. The first mine to successfully mine a strataform ore body was the Quincy Mine in 1856. The most productive deposit, the Calumet conglomerate, was opened by the Calumet and Hecla mining company in 1865. (Mine information from Wikipedia)

I’ll be excited to cut this Prehnite and make some attractive pendants.

Aliens and Salamanders

Copper Harbor (left) with sheltered harbor and Lake Superior on far left. Lake Fannie Hooe on the right. We are camped on the west side of the lake.

Today was a wonderful 75 degrees with a nice breeze. It rained during the night so we thought maybe some Greenstones would be washed out at the Central Mine. We headed out with our rock buddies Chris and Krystal, but had limited luck. There was not enough rain to wash the stones out.

It's a long way down US41 to Miami from here.

I found a rock with a drill core hole in it and forgot to take it when we left. I stashed it so I’ll get it tomorrow. I thought it would make a great planter for Bonnie. We all got a few things, but nothing to brag about. We left the Central and headed out to the logging road where Chris found his float copper the other day.

Chris again was the star, with a nice Lake Superior Agate he found where the bulldozer tracks were in the logging area. He also found a couple small pieces of Float Copper and Crystal found a small piece of float also. I hiked back into the bush and found an exposed Prehnite outcrop where I picked up a couple pieces to cut later.

These guys were digging so fast they were just a blur.

After we had lunch Chris, Bonnie, and I hiked back to the Prehnite area to dig. Krystal rested in the car as she got little sleep due to a bear roaming around their campsite during the night. We all dug, but the holes produced little except the blue spotted salamander Bonnie unearthed which was interesting to examine. It emitted some sticky substance from glands in its’ tail onto Chris. We released it so it could crawl back into a hole.
Just after that wildlife encounter the strangest alien looking bug landed on Chris. It stood still long enough for we to get a great shot of it. If anyone can ID either this Salamander or the bug, please let me know.

The Salamander. When we sprayed water on him he really was excited.

We think the "alien" is a moth. Does anyone know about this chartreuse bug?

We split up and Bonnie and I checked some outcrops on Brockway Mountain Drive for rare agates, but found none.

I think after some burgers on the grill we will go downtown Copper Harbor and be tourists tonight.

Prehnite Adventure

Monday, August 8, 2011

When you’re rock hunting you don’t always know how good the pieces are that you have found. But I spotted a promising prehnite piece today while “driving by”, that I think might be a highlight. Here’s what’s been happening.

The famous (or infamous) lift bridge separating Houghton and Hancock.

We arrived and got settled at the Houghton Campground last Thursday. The campground that the City of Houghton owns has 22 campsites for non-tent camping located right on the channel. This is a very scenic area and it is wonderfully tranquil with the occasional boat or jet ski traveling by. The channel bisects the Keweenaw Peninsula and is a shortcut from the east side of the peninsula to the west side.

Ships can pass thru the channel and when they do the lift bridge is hoisted, causing what the locals refer to as a “traffic jam”. We have been here when the lift bridge got stuck open and it really causes havoc. There is no other way to the north and the hospital is on the Hancock side, so if there is an emergency on the Houghton side (South) there is no way to get across except by boat.

U.P. Thomsonite is really ugly, but surprises await inside the ugly shell.

Today we headed out seeking U.P Thomsonite (which is pink and green Prehnite). This makes wonderful jewelry and often shows chatoyant “eyes“. When you find the stones, they are an ugly brown or bleached white and you cannot know what is inside until you cut the rind off. Picking up the right white/brown stones is the tricky part! Lots of calcite and granite show up as little white stones, but they are not of interest and I had to keep throwing them out of Bonnie’s bucket!

I'm looking for the eroded out Thomsonite.

We were with our friends Chris and Crystal. Prehnite fills voids in basaltic material, that over the years rots away and the Prehnite nodules drop out. You can dig for them in the rotted basalt, or sometimes find an eroded bank where you can simply pick them up. We filled a small bucket in short order from mostly eroded stones. We said goodbye to Chris and Crystal and decided we were done hunting for the day.

But, before we went back to the RV, I decided to explore an old logging road. I poked my head out the window, hoping to see a large agate. Chris got a big one today, and I was hoping to catch up. I saw a large seamed rock in the road and dug it up. A fantastic large seam of eyed Prehnite appeared in the rock. This was the find of the day and I think it will make some great jewelry.

A wonderful Prehnite seam.

While hunting today we found good patches of wild raspberries and Thimbleberries. No bears were about so we ate our fill. YUM!

We have not decided what is on tomorrow’s agenda yet, but we will keep blogging on our adventures here in the Keweenaw. The weather here has been ideal in the mid-70’s, but our best hunting is in the rain, so we are hoping for some soon. It has been very dry here all summer, but there was a nice shower the other night. That’s all for now.

Prehnite

Sometimes I find wonderful Prehnite on the mine dumps in the Keweenaw Peninsula.

If prehnite forms in veins, as it does in the Keweenaw Peninsula, it generally associates itself with native copper. I love to find these rare pieces that make lovely jewelry, with the apple green of the prehnite surrounding the shiny copper. prehnite-with-copper1

Most of the Prehnite of the Keweenaw is vein Prehnite. In vein Prehnite one cannot notice the chatoyant needle-like crystal structure normally associated with larger non-vein Prehnite pieces such as the gemmy pieces found in Australia and other locals around the world. Feather-like Prehnite crystals are seen in U. P. Thomsonite which is actually variegated and non-variegated Prehnite. Pink, red, and green, and other color combinations can be found, depending on what minerals flowed into the vesicles and veins along with the Prehnite. Locals refer to pastel Prehnite permeated with copper flecks found on the beaches in the Calumet, and also in the Copper Harbor area as “Patricianite”. These Prehnite pebbles can be jewelry grade, and are wonderful to collect as they roll in with the Lake Superior breakers.

Prehnite is very solid, but brittle, so care must be taken when cutting it. Stay away from new grinding wheels and rough grits. Harmonic vibrations can blow apart this material.

High quality Prehnite is available from various locations throughout the world, but when you add the native copper to the Prehnite from the U.P., you can’t beat ours.

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. Thomsonite 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.

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.