Treasures from the beaches of Sedar Bay (Part 2)

Wayne W Sukow PhD and David L Schuder BA (USA)

This is the second of three articles on the beaches of Sedar Bay. The first largely covered the geology of the area. This article will discuss collecting from the region.

Collecting Sedar Bay agates, minerals and fossils

The collection of cobbles on any beach on the lakeshore represents a distribution of materials from nearby submerged reefs and outcrops of basalts and, to a lesser extent, all parts of the entire Lake Superior Basin. There are small beaches, which are only 10 to 20 feet long and a few feet wide that are visited by collectors for the loose cobbles from the immediate reefs and surrounding basalt outcrops. Sedar Bay is large and nearly all one beach. The result is a very diverse selection of cobbles for the collector to choose from, some of them unusual and a few unique.

From Calumet and the Tamarack copper mines to the level of the lake at Sedar Bay, there’s a drop of about 1,100 feet or more. Yet, the long bay itself is shallow until you get out about 1,500 yards or further. Then, there is a steep drop off and, about 3,000 yards past that, is another deep drop off. As we’ve said earlier (but it bears repeating), the really good collecting starts at about the end of the Tamarack Water Works Road and continues to the mouth of the Black River. It also helps to know that the lake washes in and out, normally from the west or the north, while at low tide it seems to pull out from the northwest.

The cobbles on its rocky beaches seem to change several times a day and, after a strong storm, it can consist of cobbles, rocks or sand. To the experienced eye, the cobbles containing the agates all have a reddish hue and this is also a very common characteristic of the glacial gravels, far to the south of the lake, which also contain Lake Superior agates. Many of the rows of cobbles which have been sorted by the action of waves in Sedar Bay have the reddish hue as seen in Fig. 2b. Also, the different rows of cobbles have different sized cobbles, with the largest often being found highest on the beach, because gravity causes them to drop first as the incoming waves or ice recede.

The north shore of the Keweenaw Peninsula and its many beaches (both large and small) have been known and collected from for a long time. Early collectors of Sedar Bay beach pebbles may have included the Copper Country pre-history copper miners and members of the early American Chippewa and Ojibwa bands. More recently, they include Douglas Houghton’s early forays into the Upper Peninsula of Michigan, including Copper Country, which began in 1831-32 with expeditions to the territory of Michigan through the Lake Superior basin. Among other scientific work he carried out on the region, he investigated the Lake Superior copper deposits. (When the State of Michigan was established, he was appointed as the first state geologist and continued in that position until his death.) However, today it seems that there is still no comprehensive description of what one can find here. This article will hopefully change that

Today, many collectors may have a banded Lake Superior agate from Minnesota or Wisconsin, but few have seen the beauty, the many colours and inclusions of the Sedar Bay agates and its other mineral treasures. Not many who have visited have ever looked close enough to see them. David has. He has been collecting and studying these agates from the north side of the Keweenaw Peninsula for 50 years, with help of his father, Prof Donald Schuder. During those years, they have collected along many of the beaches, but they have found that Sedar Bay is the best. Unlike many other beaches on the north side of the Keweenaw Peninsula, Sedar Bay is unusual, especially in terms of the agates and other semi-precious stones that can be collected.

Besides the normal, classic red and white banded ‘Lake Superior agates’, as they’re called when found in the glacial tills hundreds of miles to the south, there are agates with inclusions of copper, silver, hematite, chalcocite, pyrite and chalcopyrite crystals, and crystals of all sizes from tiny to euhedral. David has even seen an agate from the lake that may have had gold inclusions. However, it has not been tested, so no one really knows for sure, but it certainly looks like gold and everyone hopes that it is.

David, along with early collectors, has found agates that are mostly a milky chalcedony with pseudomorph crystals and/or the mineral crystals of barite, mesolite, saponite, epidote, natrolite, prehnite, hematite, goethite, chlorite, chalcopyrite, chalcocite, tenorite, cuprite, bornite, chalcotrichite, tetrahedrite and pumpellyite. Some are shown in the images accompanying this article. In fact, Figs. 5a and b, 6a, b and c, 7a, b and c, and 10a, b and c are examples that tell the story.

On Sedar Bay beaches, you can also find the pinks, greens and whites of ‘thomsonites’ as they are called in the Keweenaw. Michigan thomsonite has been collected for many years for lapidary use. These have sagenite sprays of mesolite and natrolite, as well as microscopic crystals of native copper and silver. Some of the cuprite (reds) and tenorite (black) inclusions are larger and, when densely packed, give the stone the darker red, purple, brown and black hues. Some of the zeolites and agates have microscopic native copper crystals and, much more rarely, some have tiny silver crystals as inclusions. Fig. 8a, b and c tell the story.

As well as thomsonites, one can find prehnite nodules at Sedar Bay. These have a range of colours from white, green to pink and purples. The Fig. 9 sequence tells some of the story. Depending upon the different amount of mineral inclusions, crystal habits vary from botryoidal to euhedral similar to the zeolites. Some of the prehnites have native copper and silver as inclusions.

Early collectors were creative and liked to give descriptive names to the different types of agates they found. Among those they described are banded, fortified, ruined, disrupted, eyed, cloud, dendritic, moss, lace, shadow banded, flame, fire, confetti, plume, sagenite, curl, pastel paint and carnelian, with any number of possible combinations in the same agate or stone from Sedar Bay. All come as tumbled cobbles by themselves or in situ in the tumbled basalt matrix cobbles. Some show plumes of other minerals forms and the Fig. 10 sequence tells this story.

Along with agates, collectors have found jaspers that are granular and banded. Some have areas of fortifications, plumes and dendrites, and a few are silvery black – the result of metallic hematite. These inclusions suggest that they may have originated in the iron rich areas of the Gunflint Range in Canada and/or Michigan’s Iron Ranges to the south of the Copper Country. Also among the jaspers are the granular ones, which look like algae with hematite inclusions. Fig. 11a, b and c show a few examples.

We believe the diverse array of Sedar Bay polishable pebbles reflects the geological history of the lake. Over time, many different minerals, combinations of minerals and the matrix containing them were brought into the Lake Superior Basin by the many glaciers that have passed over the Keweenaw Peninsula and the lake itself. It is tempting to look at the relative abundance of the different varieties – such as the disrupted, fortification and plume agates illustrated in this article – as having some significance. However, it’s likely that the distribution simply reflects our personal likes and dislikes.

The pictures

Fig. 4a. A beautifully coloured and patterned fortification copper replacement agate, which has many small crystals of copper in some of the banding. The copper can be seen without magnification as the pink and purple bands on the upper left. It looks like a Kearsarge Lode mine agate. (From the Collection of Wayne Sukow.)

Fig. 4b. Perhaps the rarest Lake Superior agate found to date comes from Sedar Bay. Nestled in a small depression is a 4mm ball of silver crystals that penetrates into the agate. The outer edge of the ball is prickly, with well-formed silver crystal tips, while the inside is a solid mass of silver. As far as we are aware, this is the first reported occurrence of native silver in a Lake Superior agate. (From the collection of Wayne Sukow.) However, in the Sukow collection of copper agates, there are several that also have small blebs of native silver. These have not yet been reported or shown in a public forum.

Fig. 5a. Native dendritic copper crystals are disseminated through this pink chalcedony nodule, with a few native silver inclusions. These are striking and, while rare among Sedar Bay agates, it provides clear evidence that copper agates are not limited to the Wolverine #2 mine on the Keweenaw Peninsula.

Fig. 5b. Any collector would recognise this as a Lake Superior agate, with its unusual rich, orange-rust colouring and some thin white bands. Its structure is complex, with fortification bands, lacy patterns, quartz and tubes. The husk has been ground away.

Fig. 5c. The brown and mauve-grey colouring is unusual in this strikingly patterned agate. A thin reddish husk outlines the bottom and a small amount of matrix remains attached.

Fig. 5d. Again, any collector would recognise this as a Lake Superior agate in the rough, with the classic red, white and clear fortification bands that are their hallmark. (From the collection of EV and Sue Duester.)

Fig. 5e. Opaque orange, cream and tan bands characterise this agate. The numerous, dark rusty-red areas follow fractures in it and the colouring is caused by iron rich compounds seeping into them and staining the nearby chalcedony in this ‘paint agate’.

Fig. 5f. The very irregular shape on the outside of this agate indicates it comes from a ledge or reef near the bay, and has not been tumbled and ground by long exposure to the waves of the lake. It was found in a sand dune and is known locally as a ‘water level’ agate.

Fig. 5g. Sprays of white, needle-like crystals make up this agate, which collectors call sagenitic. It looks like it consists of mesolite crystal sprays.

Fig. 5h. The black inclusions in this chalcedony nodule are not actually long crystals. A microscopic examination reveals that they are a linear array of tiny black crystals with a high lustre of chalcocite. (ID by Dr George Robinson.) The fibrous appearing quartz may be Fadden quartz, where the stress present during its formation is revealed by a fibrous appearing structure. The stone is unpolished since we did not want to lose the chalcocite crystals.

Fig. 5i. A ‘ruin agate’, so named because the broken fortification band fragments appear to be jumbled and then bonded together by fresh chalcedony.

Fig. 5j. Four years ago, David walked to the lake in front of his lake house and found an agate lying on the beach. When he got back to the house, he remembers saying, “The Lady of the Lake was good to me today”. It has since been polished at angles to show off the stone better. He says it’s one of the better ‘lakers’ he’s found to date. He obtained three stones out of that one agate.

Fig. 5k. The sharp-edged inclusions appear to be grey basalt and rusty pieces of another mineral. In several places, there also appear to be some small fortification bands of a greyish colour. The enclosing white cementing material polishes well and appears to be chalcedony.

Fig. 5l. This is a ‘shadow banded agate’ that looks like a cross section of a skull and, in the eye socket, looks to be a face with two eyes, nose and mouth. The orange and reds are from iron oxides.

Fig. 5m. An array of randomly oriented (jackstraw) brownish, rusty-orange and grey, needle-like natrolite crystals in white chalcedony. (ID Dr George Robinson.)

Fig. 5n. Is this another disrupted Lake Superior agate? With its rusty-orange aggregates plus some blue-white chalcedony in the in-between spaces, it is very striking. The rusty-orange needles are healed fractures showing the iron oxide-rich solutions that penetrated them. There is some metallic, dull, silver-ish hematite in the polished face.

Fig. 5o. If the agate were rotated by 90⁰, red and white stalactites would be hanging down into a cavity now filled with quartz, making it an awesome stalactite tube agate with lacy pattern banding.

Fig. 5p. The sharply defined banding with the clear chalcedony between the white bands is an outstanding shadow agate.

Fig. 5q. Spherulitic patterns with white needle crystals radiating in this off-white and tan prehnite nodule, with a few native copper blebs.

Fig. 5r. The rust-orange colour is uncommon in the agates of Sedar Bay, unlike the agates found in situ in much of Upper Michigan’s Copper Country. Here, it colours the sagenitic mesolite crystal sprays that point inward from around the outer edge. The reddish-brown hue at the tips indicates some mixing with iron oxide or hematite. (ID Dr George Robinson.)

Fig. 5s. Prehnite crystals vary from white to pink. The pinks are from microscopic copper crystal inclusions. There is also an area of fortified banded of chalcedony coloured blue by bornite. (ID Dr George Robinson.)

Fig. 5t. This is a nice close-up, with a hint of microscopic native copper inclusions around the fortification banding of prehnite and chalcedony. The mixture of prehnite and chalcedony raises the question: is it an agate hybrid? The prehnite-chalcedony combination is also seen in some of the copper replacement agates from the Wolverine #2 Mine.

Fig. 5u. Shades of blue bornite can be seen here. There are delicate, light blue, innermost crystals lining the cavity, which are supported by a thin, dark blue-green band. On the right in the centre, there also appears to be a hint of fortification bands. The microscopic native copper inclusions around the fortification banding are easily seen. It’s an amazing Sedar Bay treasure.

Fig. 5v. This is another curious, prehnite-chalcedony agate, with radiating clusters of prehnite with orange-ish iron oxide centres. The greens are from chlorite inclusions.

Fig. 5w. Here is an unusual combination of materials. It suggests a disrupted agate, but look closely. At several locations, there are hexagonal structures (quartz crystal pseudomorphs) with some of them distorted. Are they skeletal crystals or some replacement? The dark material may be goethite, since it lacks the silvery black lustre of polished hematite.

Fig. 5x. Pale purple angular areas are enclosed by rectangular platy crystals of barite or some replacement quartz after barite. Amethyst agates are very rare from Sedar Bay.

Fig. 5y. A Lake Superior paint agate, with fortification banding and red iron oxide centre, with a vent tube showing.

Fig. 5z. Recognisable as a Lake Superior agate, this one has an unusual combination of patterns from pattern-less and jasper-like, to fortification bands and red and white internal hemispheres. What theory of agate formation explains how these originated?

Fig. 6a. Here are some more rectangular, flat, platy crystals with a light orange (perhaps adularia?) outer case and dark green chlorite material inside. This suggests replacement after barite. A careful study of the photo reveals several rhombohedra or parallelogram crystal structures, showing a cross section of the barite crystals. The white areas are chalcedony, which can also be seen between some of the crystal replacements.

Fig. 6b. Natrolite crystals in chalcedony with the rusty-red iron oxides. The brassy-yellows could be from chalcopyrite and there are a few blebs of native copper floating about the agate. (ID Dr George Robinson.)

Fig. 6c. A perfect, pinkish oval Lake Superior ‘eye agate’, with multiple sharp, outer bands and lacy bandings.

Fig. 6d. In contrast to the agate on its left, this eye agate shows only red and white colouring, with no sharp outer bands.

Fig. 6e. Is this a jasper-agate? The deep brown with a reddish hue appears opaque, but the circular fortifications bands in the eye are not. And neither are the semi-circular, white fortification patterns on the top or in the crystal replacement on the lower right and top. The reds are from iron oxides and the light blues are from bornite. The fractures appear to be healed, which is typical of some of the Copper Country agates found and mined from ledges on the inland bluffs. (ID Dr George Robinson.)

Fig. 6e1. Another disrupted agate with a variety of inclusions, which looks to be barite.

Fig. 6f. There are striking rhombus shapes with deep rust-red and green blue interiors in this specimen. Of course, the rhombus shapes are typical of the calcite crystals in this region, so we interpret these as replacements after calcite. The dark rusty-orange outer band may be iron oxide or the reddish-orange cupric oxide. There are a few blebs of native copper in the stone. The suggestion of cupric oxide follows from the green and blue of the interiors as seen in Fig. 6h.

Fig. 6g. Another area on the previous agate shows the same replacements after calcite.

Fig. 6h. At even higher magnification (16X), the blue and blue-green of the interior crystal replacement are easily seen. Perhaps it’s the blue copper mineral bornite or a bornite-malachite mix. From the structures on the inside of the replacement area, it’s hard to tell.

Fig. 6i. Again, there’s a similar blue-green mix of minerals in a close up photo of another Sedar Bay agate. The mineral mix happened more than once. The bright yellowish mineral is limonite, while the brownish sections are natrolite crystals stained by goethite or iron oxide. (ID Tom Rosemeyer.)

Fig. 6j. Shades of the crazy lace agate pattern in a Lake Superior agate are unusual. Here’s one from Sedar Bay. The reds are iron oxides and the browns goethite, and there are some metallic hematite inclusions about.

Fig. 6k. A classic red and white Lake Superior agate, with an interlocking quartz crystal interior plus some fortification. The reds and bright orange-reds are from iron oxides.

Fig. 6l. An unusual, well-tumbled, translucent shadow-banded fortification agate with an eyeball.

Fig. 6m. “Weathered and beaten” may best describe this agate. The brownish curlicues show fortification banding, as do the white areas, which may be surface oxidation or could be white opal. Much of the agate seems to be filled with unstructured white and light tan chalcedony, so we suggest it be named a ‘disrupted ruin gate’.

Fig. 6n. A classic Lake Superior agate with its light brown, white and clear fortification pattern.

Fig. 6o. An odd agate for Sedar Bay or anywhere. It shows a lacy banding of dancing flames of white in a salmon-red chalcedony. There are a few native copper inclusions around the outer rim.

Fig. 6p. Greenish and grey minerals, and native copper flecks in white chalcedony, distinguish this agate. Apparently, whatever drives pattern formation never occurred in this disrupted agate.

Fig. 6q. Another disrupted agate. Many of the Sedar Bay agates seem to fall into the disrupted category. Why? Are they pieces of agate broken from chalcedony seams, which have become more or less rounded due to the tumbling action of the waves that move them about the bottom of the lake?

Fig. 6r. A classic opaque pink and orange paint agate, common to many Copper Country localities. Many paint agates have triangles in the centres with reddish spheres or dots.

Fig. 6s. This really looks like a piece of seam agate that’s been tumbled. The orange to yellow to brown ‘mountain’ patterns are formed by fine needles of varying length. The fine white tips on the needle-like, mesolite crystals are really stained iron oxides and limonite. The central band is quartz. (ID Dr George Robinson.)

Fig. 6t. At first glance, this seems to be a disrupted agate, but with a longer look, you can see thin white rectangular needles throughout the entire agate. It is known as ‘Jack Frost agate’. The reddish and blackish areas are amorphous aggregates of the red and black iron oxides.

Fig. 6u. Is it a breccia agate? Mottled matrix, some of which is angular, is seen on the top and bottom. The red and white pattern on the top seems to be sagenitic in structure and polishes as chalcedony. The reds look to be from microscopic copper inclusions and one of its oxides. The light tan inclusions are a mystery.

Fig. 6v. A pastel tan agate that has been well tumbled. It is also fracture free, which is fairly common for Sedar Bay agates. This contrasts with those that have been moved by glaciers in the gravels far to the south of Lake Superior.

Fig. 6w. A one-eyed ‘Smoky the [agate] Bear’ in typical Copper Country light tan, with a quartz body.

Fig. 6x. A frilly fortification banded Sedar Bay agate in matrix, which are few and far between.

Fig. 6y. A mixture of gorgeous pinks, reds and purples on a light blue background, which are pleasing to the eye and give this hematite plume agate a unique character. This is a very rare find for any Lake Superior agate. (From the collection of the Seaman Museum – donated by David Schuder.)

Fig. 6z. A flawless, translucent agate, with subtle fortification bands.

Fig. 6zz. Mesolite, needle-like crystal sprays that have microscopic native copper inclusions in prehnite. The brassy-yellow stains look to be from chalcopyrite. (ID Dr George Robinson.)

Fig. 7a. In contrast to the previous agate in Fig. 6z, this is another of the typically opaque Copper Country agates, with its pastel coloration and a triangular centre, fortification banding and a vent.

Fig. 7b. The rounded edges of this agate suggest it’s from a seam and has been well tumbled. The reddish and brownish needles seem to extend through the faint white and clear fortification bands. The brownish needles indicate that they are a mixture of red iron oxide and black hematite.

Fig. 7c. Merry Christmas – as we have red, white and green. It’s another blockish agate with edges rounded by tumbling action. The green material in some bands and the larger central area give it a distinctive character. The few small, dark brown and red areas are amorphous aggregates of red iron oxide and black hematite, and the greens are from chlorite or pumpellyite.

Fig. 7d. A ‘floater’ Lake Superior agate has red fortification banding surrounded by quartz and containing quartz in its interior. The agate shown meets the classic definition of a floater agate.

Fig. 7e. Another unusual Sedar Bay agate, with soft grey-lavender fortification bands, massive white to light-orange chalcedony, a transparent area and small curls of moss and columns on some areas of its edge. It also has shadow banding, which gives great chatoyancy.

Fig. 7f. Thin rectangular crystals and barite, along with various shades of reddish iron oxide amorphous aggregates are embedded in a whitish chalcedony. It’s just another typical Sedar Bay agate treasure.

Fig. 7g. A disrupted Sedar Bay agate, with some unusual and unknown structures in its interior. Do they look like cell structures?

Fig. 7h. It’s always reassuring to find another ‘typical’ Lake Superior agate among those found on Sedar Bay beaches. The very translucent, red-orange filling of the white rimmed eyes is interesting.

Fig. 7i. Another multi-eyed agate with very subtle pink hues in its outer rings. The contact lines between the eyes that meet are short, straight segments, similar to the contact lines between the bubbles we all blew as kids.

Fig. 7j. Another disrupted prehnite nodule with copper inclusions. The greens are from copper carbonates, with interesting coloured and amorphous aggregates of varying sizes.

Fig. 7k. This disrupted agate of greys and white chalcedony, with a variety of crystal specimens above, contribute to the view that many Sedar Bay agates are unusual, if not unique. This may be dolomite with other inclusions brought in by one of the many glaciers.

Fig. 7l. Mesolite needle-like crystals, which are full of microscopic native copper inclusions in a milky white and clear chalcedony, give this nodule its colour. The matrix is a dark green chlorite and quartz mixture with coppers. (ID Dr George Robinson.)

Fig. 7m. There was only a little tumbling in the history of this agate, since it retains its irregular surface and a husk on more than half the outer surface. The multi shades of grey interior are unusual and would make an interesting microscopic study. The lace type fortification banding and blue shades may be from bornite.

Fig. 7n. Massive, rusty-coloured iron oxide and black hematite aggregates seem to be welded together by translucent orange chalcedony. There are metallic hematite inclusions and nice lacy, fortification banding, and some mesolite crystals.

Fig. 7o. A complex, disrupted agate, with multi mineral inclusions, with a few small eyes and areas of fortification banding. The reds are from iron oxides and the yellows are from limonite/goethite, and there are a few tiny blebs of native copper.

Fig. 7p. You’ve seen this agate earlier (Fig. 4b), but it is so rare that it deserves repeating. The reverse side of this nodule has a deep red fortification pattern, which pales by comparison to the translucent red chalcedony of this side, which has several chunks of silver protruding from it. The most prominent is a silver ball, which has distinct crystal tips. As noted earlier, this is the first published statement reporting the occurrence of crystallised native silver in a Lake Superior agate. (Collected by Donald Schuder and currently in the Wayne Sukow collection.)

Fig. 7q. Another view of the ‘silver agate’, which is a true treasure of Sedar Bay.

Fig. 7r. Varying length tubes or needle crystals in a grey translucent chalcedony are the hallmark of this Sedar Bay agate. It looks like a crystal garden.

Fig. 7s. Another complex disrupted agate, with multi mineral inclusions. It includes small flecks of silver, along with copper and chalcopyrite.

Fig. 7t. Another disrupted Sedar Bay agate, with amorphous dark brown to varying shades of rusty-red iron oxide aggregates.

Fig. 7u. Embedded in grey chalcedony is a jackstraw arrangement of some minerals [after][?] platy barite crystals. The yellow case may be the iron mineral limonite and the rust-red may be iron-oxide aggregates. There are microscopic copper inclusions in a few areas.

Fig. 7v. A fine example of a disrupted Lake Superior red iron oxide agate. Some collectors call this type of agate a ‘cloud agate’. It has really been shaken up and vibrated in a semi-liquid state.

Fig. 7w. Here are many tubes, spheres and eyes in a root beer chalcedony. There are several bright, metallic, square-ish inclusions of pyrite. (ID Dr George Robinson.)

Fig. 7x/7y. This agate has moss-like growth of different colours from various mineral inclusions and influences in the clear-to-translucent chalcedony. There are pyrite crystals in six small areas, which is very uncommon in any Lake Superior agate. (ID Dr George Robinson.)

Fig. 7z. A tube agate with halo spheres around a few of the tubes, which makes them look like candles with flames. (From the collection of Sam Norwood.)

Fig. 7aa. Bright reds, yellows and orange colours in this moss agate. Some of the growth looks like coral rather than a mossy/plume-type growth habit, along with areas of fortification around translucent chalcedony.

Fig. 7bb. Moss agate – the brown moss colours are from goethite in the translucent chalcedony, and the yellows and oranges are jasper. Some have suggested they may be opal (hardness ~5), but since they don’t undercut when grinding and polishing the surrounding chalcedony, they have essentially the same hardness as chalcedony, which means they’re definitely jasper.

Fig. 7cc. Chlorite (dark green/black) and chalcedony surround these odd-shaped, metallic crystals. It is ilmenite altered to titanite. (ID Dr George Robinson.)

Fig. 8a. A striking arrangement of green, pink-to-white spray of needle crystals resting on a basalt matrix, with a few bits of native copper, begin this portfolio of Sedar Bay’s mineral treasures.

Fig. 8b. A striking, single spherulitic spray of needles make this thomsonite, with its rose-pink to hints of green hues. Michigan Lake Superior thomsonites are a mix of mesolite, thomsonite, prehnite and natrolite.

Fig. 8c. This nearly complete nodule of thomsonite, with rich, rose-red sprays of needles trimmed in green, is quite a contrast to the colours and hues of agates. They are a Sedar Bay treasure.

Fig. 8d. Another complete thomsonite. This nodule, with a different pattern, is beautiful with its rich, rose-red sprays of needles trimmed in green and white, with copper inclusions.

Fig. 8e. A close-up of thomsonite needle crystal sprays. The dark rust-brown hue is unusual since it is full of microscopic and larger, native copper crystals.

Fig. 8f. Shades of purple, white and green in a thomsonite confined to develop in an irregularly shaped cavity. This show that there is no husk associated with their formation or pattern, which mimics the cavity’s shape. There are microscopic native coppers in the stone.

Fig. 8g. Another striking thomsonite, with a single spherulitic spray of needles with rose-pink-to-hints of green hues.

Fig. 8h. A rose-red and black, triple spray thomsonite.

Fig. 8i. An unusual, deep green and white thomsonite nodule. On the top and upper left, there seems to be a dark green chlorite cap of matrix.

Fig. 8j. Another green and white thomsonite, with smaller sprays of needle crystals. Perhaps they are simply mesolite.

Fig. 8k. Another striking single spherulitic spray of rose-pink needles. What is the black dot in the centre?

Fig. 8l. Another striking thomsonite, with a single spherulitic spray of needles, with rose-pink and a few green-black sections.

Fig. 8m. A Lake Superior thomsonite. Some see a cat, some see an owl, others a raccoon. However, there is definitely a pair of eyes, a nose and great colours in the sagenite sprays of these crystals of mesolite, thomsonite, prehnite, copper and natrolite.

Fig. 9a. Prehnite crystals with colours from the reds of cuprite to the whites and greens of prehnite and copper carbonate, and lots of microscopic and larger copper crystal inclusions.

Fig. 9b. Prehnite with botroyidal whitish crystal tops, in an apple-green prehnite matrix, with native copper inclusions.

Fig. 10a. This specimen appears to be a chunk of seam dendritic agate, with a thin layer of matrix on the top and bottom. Edges and corners are rounded, which is evidence of tumbling action.

Fig. 10b. A close-up of the previous photo shows small, brownish plume fronds. The brown mineral that constitutes the plumes is goethite. (ID Dr George Robinson.)

Fig. 10c. The flat border between the agate and the matrix on the bottom suggests that this too started as chunks of seam agate or a broken amygdule.

Fig. 10d. In the close-up, gorgeous purple plumes are seen with each group being isolated in a cell with a white chalcedony border. The diffuse yellow seems to have its own cells and inhibits the growth of the plumes. There are microscopic native copper inclusions in the plumes and the deep reds look to be cuprite.

Fig. 10e. A ‘moss agate’ with small curlicues of dark brown and a few dark red mineral aggregates imbedded in an opaque rust-orange chalcedony. On the lower right, several fortification bands can be seen.

Fig. 10f. In breccias and ruined Lake Superior agate, there are bands that have been broken up and moved around the inside of the stone, with fracture lines that have been re-cemented.

Fig. 10g. A beautifully patterned jasper-agate, with small, red iron-oxide plumes on the polished surface and pink fortification bands inside lacy, island-like structures.

Fig. 10h. Strands of red-orange and brownish iron oxide cause the filaments of moss in the off-white chalcedony.

Fig. 11a. Again, we seem to be looking at a chunk of jasper that originated in a seam, with its edges rounded by tumbling. The rust-red, horizontal layers are iron oxide – the red kind – and the black layers are hematite.

Fig. 11b. The rust-red plumes are the red iron oxide and the black background is hematite – the black iron oxide. Notice that both varieties are dense, hard and take a very good polish.

Fig. 11c. The large black eye on the outer part of a white chalcedony agate is unusual. The diffuse orange-red underneath is dense, red iron oxide and the black is metallic hematite in the bands of the eye.

Fig. 11d. Black hematite plumes with dull, silver-ish, metallic flash in an off-white and translucent chalcedony.

Fig. 11e. Dainty red, iron oxide plumes, with a black hematite centre, give a striking pattern. Set in white chalcedony, they nicely frame the interlocked quartz crystal centre of this agate.

Fig. 11f. Small reddish rosettes/florets of iron oxide in a white translucent chalcedony.

Fig. 11g. A piece of white chalcedony agate, with a dense, reddish outer edge of iron oxide. Its shape suggests it is a tumbled piece of seam agate.

Fig. 11h. A nodular agate, with a large area of dense red iron oxide, which shows no evidence of being aggregated. The remainder of the piece seems to be disrupted moss agate.

Fig. 11i. Another white chalcedony agate, with black hematite plumes mixed with dark-brown plumes, which are a combination of aggregates of the red iron oxide and the black hematite. The included grey chunk on the right with angular corners is a brecciated fragment.

The next article in this series covers collecting fossils from the Sedar Bay area.

Acknowledgements

All but a few of the Sedar Bay mineral treasures shown in this article were collected by Dr Donald Schuder (deceased), who taught at Purdue University, his wife Mary and his son, David Schuder, who is co-author of this article. Also, Sam Norwood’s Sedar Bay collection is well represented.

We are indebted to Dr George Robinson, curator of the Seaman Mineral Museum at Michigan Technological University, Dr Gene LaBerge, geologist at the University of Wisconsin-Oshkosh, and Tom Rosmeyer, the former geologist at the Camp Bird Gold Mine in Colorado. Thanks also go to John Marshall, who started all this a few years back and his editing skills. All photo images are by David Schuder.