MINERAL OF THE MONTH: December 2017 – Septarian Nodule

Septarian nodules are round concretions found in sedimentary rocks. Concretions are hard solid masses formed by the accumulation of matter within sediment. Although scientists do not agree on the details and specifics of their formation, there are several theories. One proposal suggests they formed when there was dehydration and shrinkage of clay, gel, or organic cores within sedimentary pockets. Others believe there was an expansion of gases produced by the decay of organic matter that fractured material within sedimentary pockets. One more theory is that an earthquake, compaction, or other geologic forces fractured material within sedimentary pockets. However the sedimentary material fractured, mineral-rich fluids filled in the spaces between the fractures allowing calcite, siderite, pyrite, and other minerals to crystalize and fill in the open areas within the cavity.

The most well-known septarian nodules are found in Utah. The Utah septarians developed during the Cretaceous period between 50 and 70 million years ago. At this time the Gulf of Mexico had expanded northwest into the area that is now southern Utah. Scientists believe that volcanic eruptions killed marine organisms, causing them to sink to the bottom of the shallow sea. The decomposing material chemically attracted sediments causing the mixture to form into mud balls. When the ocean receded, the mud balls dried out causing the interior sections to crack and shrink. Over time, mineral-rich solutions infiltrated the cracks causing crystals to form and fill in the cracks. Septarian nodules, sometimes called lightning stones, can also found on the Lake Michigan shoreline as well as in New Zealand, England, Morocco, and Madagascar.

Septarians are composed of calcite (the yellow centers), aragonite (the brown lines), and limestone (the outer grey surface).  Occasionally, fossils can be seen within or on the surface of the nodules.



NOTE: More Grand Marais scenes are posted often on my blog at www.agatelady.blogspot.com and on my main personal Facebook page listed under Karen Ann Penegor Brzys.

For this webpage update, I have selected some of my favorite pictures that I took in the Grand Marais area between August and November.

To begin here are a couple of fall photos. The first was taken from the Log Slide area looking toward Au Sable Point in the Pictured Rocks National Lakeshore. The second was taken during a hike on the White Birch interpretive trail above Twelve mile Beach Campground.


While at the Twelve Mile Beach Campground I also captured a sunset photo.


On another fall hike in the national park from the Log Slide to the Hurricane River, I captured this picture of the lighthouse.


The photo below was taken on the same hike. It shows the mouth of the Hurricane River looking west. Grand Island, located in Munising Bay, can be seen in the background.


This year we have had more high wind events than you can count. During one storm I drove east of town, hiked to the shoreline, and captured this image.


The third week of October we had some of the largest waves ever recorded on Lake Superior. One wave was 28.8 feet high, as measured at a buoy located north of Munising. As a result, the shoreline erosion was intense. There are sections of the beach that are no longer passable unless you walk in the water. At other points, the driftwood just piled up as can be seen in these two photos taken at First Creek, located just west of Woodland Park in Grand Marais.


We have had a couple of early snowfalls, but as of the end of November, all the snow has melted. Here are a couple of photos I took just after one of the early snowfalls.


MINERAL OF THE MONTH: July 2017 – Kona Dolomite

This rock is named after the Kona Hills, located in Marquette County, Michigan. This is an ancient formation of fossil stromatolite that is between 2.1 and 2.8 billion years old. Most dolomite found throughout the world is gray or white. Kona dolomite is quite colorful and is found nowhere else. Dolomite is a calcium-magnesium carbonate and fizzes in warm acid.  Dolomite is limestone with magnesium added. The Kona formation is dominantly dolomite with interstratified layers of shale, graywacke and quartzite. The dolomite beds are from a few inches to many feet thick, but even the purest beds contain thin cherty layers and other sedimentary clastic material.

The original organisms that created this fossil rock were some of the first life on earth. There was nothing to eat so these early cyanobacteria survived by using the energy of the sun via photosynthesis. Cyanobacteria were responsible for producing the first oxygen on earth as a byproduct of this photosynthetic process. Thus, if it were not for stramatolitic organisms, according to scientists, we would probably not be here.

The cyanobacteria grew in shallow water as flat mats to maximize exposure to the sun. The fossil rock formed as the cyanobacteria mats trapped, bound and, and cemented sedimentary grains. Over time, as the trapped sediments blocked the energy of the sun, the cyanobacteria would develop another mat on top of the mound. The mounds grow in various shapes including conical, stratiform layers, branching, and domal.

The earliest stromatolite mounds are believed to be 3.7 billion years old. They peaked around 1.25 billion years ago. Originally scientists believed these species of cyanobacteria were extinct, until live stromatolite mounds were discovered in Sharks Bay, Australia in 1958. Even though 99 percent of all species that have ever existed on earth are extinct – it is amazing that stromatolitic organisms were the first living things on earth – and they are still here. Living stromatolites mounds can be found in Australia, Chili, Brazil, Mexico, Belize, British Columbia and the Yukon (Canada), Minnesota (US), South Africa, and the Bahamas. In modern microbial mats, debris from the surrounding habitat can become trapped within the mucus, which can be cemented together by the calcium carbonate to grow thin laminations of limestone.

Fossilized stromatolite rock can be found throughout the world. Kona dolomite is one example. Because of its tremendously old age, and due to trace minerals, Kona dolomite can be found in a variety of colors including pink, brown, yellow, tan, cream, red, and orange. The colors are often complex with mottling, banding and lacing. The black wavy lines in Kona are the remains of the microbial mats. The unique pink and red pigments are caused by the iron in the soil.

In the rough before polishing the rock does not look nearly as nice – but still cool.

Lapidary enthusiasts enjoy working with this rock because they make beautiful slabs used in crafting clocks, wind chimes, spheres, bookends, cabochons, and other items. Kona is also used for building stones and for making refractory bricks for furnace linings. Due to its vivid coloration it is also used for decorative purposes as crushed stone for borders and walkways.



  • Thanks to Bob and Peg Clark for their donations of Kona dolomite specimens and slabs to the Gitche Gumee Museum.


NOTE: More Grand Marais scenes are posted often on my blog at www.agatelady.blogspot.com and on my main personal Facebook page listed under Karen Ann Penegor Brzys.

For this webpage update, I have selected some of my favorite pictures that I took in the Grand Marais area between the end of March and mid-July.

First, here are a few early spring photos. The first one was taken from the break wall at the end of Coast Guard Point. The second was taken from a bluff in the Grand Sable Dunes.

During late spring when I arrived home, as I drove up my driveway I was greeted by a fawn.

In June we had a lot of rain. One Sunday Grand Marais received five inches. Driveways were washed out, my road was closed due to a sinkhole, other roads were washed out, and the cemetery east of town flooded.

As of mid-July, the level of Lake Superior is 602.89 feet above sea level. This is ten inches above the all-time average for July and only two inches below the all-time recorded high level for the month of July (1950). The current level is 31 inches above the all-time recorded low level for the month (1926). The high water level combined with the increasing number of wind events has caused extreme erosion to the shoreline. East of Grand Marais some of my favorite beaches are no longer accessible since the erosion has formed sand escarpments.

The Grand Marais July 4th celebration was again a great success. The weather cooperated with sun and temperatures in the upper 60s. It was cool enough to allow me to wear the 1800s U.S. Postal Service bear coat and mittens in the parade. The museum founder, Axel Niemi, wore the coat every year, but I only do it when it is cool enough. The firework display was also fantastic!

We have had a lot of great sunsets already this year. In the picture below I used my zoom lens to get a close-up.

I have been doing a better job this summer getting exercise than I have in past summers, but I still do not get out enough. I have gone on several hikes in the Grand Sable Dunes. The following photo was taken from near Sable Lake looking north to the big lake.

In mid-July, I went on a solo hike in the Log Slide area. Unfortunately, the erosion problems took out the platform at the Log Slide. So far the National Park Service has not made repairs. Although the trail to the platform is not open, the North Country trail east and west of the Log Slide is open. The Log Slide itself is also open, but people should take extreme caution going down since there are sections with clay escarpments. The photos below were taken during my Log Slide hike.


MINERAL OF THE MONTH: March 2017 – Chert

Chert is a microcrystalline or cryptocrystalline sedimentary rock made mostly of silicon dioxide (SiO2). It can form as nodules, concretions, and as layered deposits. Like other silica rocks and minerals, chert breaks with a conchoidal fracture, often producing very sharp edges. Native Americans took advantage of this fracture pattern and intentionally knapped chert to make arrowheads and other cutting tools and weapons. Since chert forms in sedimentary rock, it often can contain fossils as well as banded layers.

There are two main ways chert forms. In some cases, chert develops when microcrystals of silica grow in deposits of limestone or chalk. This occurs when dissolved silica is transported through sedimentary layers by groundwater. Large numbers of silicon dioxide microcrystals grow from the dissolved silica into irregularly-shaped nodules or concretions. If there is a lot of silica causing large number of nodules to form, the nodules can merge together to develop a contiguous layer of chert within the sedimentary rock. When chert develops from dissolved silica it is classified as a chemical sedimentary rock.

The other way chert forms is from biologic remains. Certain marine organisms contain silica in their exoskeletons or spicules, such as sponges, radiolarian, and diatoms. When these organisms die, their remains fall to the bottom of the oceans or shallow seas. The silica dissolves, recrystallizes, and develops into chert nodules or entire layers of chert.

Most chert is tan, cream color, or gray. When iron impurities are included within the nodules or layers, chert can also be red, green, or black. In some cases red chert, or chert with other colors, is classified as jasper. The term “flint” is used to describe varieties of chert that form in chalk formations, whereas chert usually forms in limestone formations. Some people make a distinction between “flint” and “chert” as a matter of quality – chert being lower quality than flint. Sometimes jasper is also considered a higher quality of chert.



NOTE: More Grand Marais scenes are posted often on my blog at www.agatelady.blogspot.com and on my main personal Facebook page athttps://www.facebook.com/karen.brzys.

For this webpage update, I have selected some of my favorite pictures that I took in the Grand Marais area between September and February.

First, here are a few fall photos.

One of the first snow storms we had coated everything with white.

Finally, here are some winter photos, including one photo from the UP 200 Dog Sled Race. The mushers stop, rest, and turn around in Grand Marais.

MINERAL OF THE MONTH: June 2016 – Lake Superior Copper Replacement Agates

This web page update features the copper replacement agate. They can only be found in the Keweenaw Peninsula, located in Michigan’s Upper Peninsula. They can be found in the mine dumps near abandoned copper mines from the Kearsarge Lode. Most of these agates are small – less than an inch in diameter. They are extremely rare and difficult to find, usually requiring labor intensive work to free them from the basalt matrix rock. These agates are well sought after because of their rarity, their interesting patterns, and the vast array of other mineral inclusions. In addition to copper these agates often have other mineral inclusions including silver, calcite, malachite, tenorite, epidote, and pumpellyite, In most cases these small agates are fully husked, requiring them to be cut to expose their inner beauty.

The copper replacement agate shown below includes malachite, pumpellyite, and epidote inclusions.

The agate below has white chalcedony bands on the left and clear calcite on the right. Copper is in the outer shell, surrounding the specimen. The green is epidote and the red is a copper oxide.

The two photos below show copper replacement agate nodules in basalt matrix rock. In addition to copper there is also prehnite, epidote, and pumpellyite (dark green inclusions). These photos were taken by Dave Schuder.

The specimen shown below has basaltic matrix on the left and copper replacement on the right. The copper bands alternate with the chalcedony bands. This photo is from my agate book, Agates Inside Out.

CITATION: The first three photos shown above (used with permission) are from the Wayne W. Sukow collection http://www.sukowssuperiorminerals.com.


NOTE: More Grand Marais scenes are posted often on my blog at www.agatelady.blogspot.com and on my main personal Facebook page at https://www.facebook.com/karen.brzys  . I also post agate photos, shared mostly on various Facebook rockhounding sites, to the museum’s Facebook page at https://www.facebook.com/pages/Gitche-Gumee-Agate-and-History-Museum.

For this webpage update, I have selected some of my favorite pictures that I took in the Grand Marais area between December and June.

First I will include several winter photos. The first picture was taken near First Creek, located on the west side of Grand Marais. The weather this day was well below zero with 40 mph winds!


The next photo was taken from the boat ramp on Sable Lake, located in the Pictured Rocks National Lakeshore.


I love exploring the Grand Sable Dunes every month of the year, but I think it is most beautiful in the winter.


Lake Superior did not freeze over this past winter, but there were huge shelf ice formations and ice volcanoes near shore!


The next two photos document how deep the snow gets in Grand Marais during the winter.



Us yoopers love the snow!


While skiing on the beach late winter, we came across a local resident.


In the early spring shelf ice hugs the Lake Superior shoreline.


The spring in Grand Marais is steelhead season. The photo below shows a couple of local fishermen trying their luck at the mouth of the Sucker River, located east of Grand Marais.


The photo below shows a pond that is located on the beach east of Grand Marais.


MINERAL OF THE MONTH: November 2015 – Slag

Throughout the past 17 years since re-opening the Gitche Gumee Museum (after it was closed by its founder 21 years previous), each summer many people bring pieces of slag in for identification hoping that the specimens are agate. Slag can be found on the beaches west of Munising, MI, as well as at several other places in Michigan in other areas where blast furnaces were used to purify ore. I can understand why people think these specimens are agate since oftentimes like agates; they have conchoidal fractures, structure or other patterns, and translucency. I have learned over the years how to let people down easily and educate them at the same time.

Originally there were 29 blast furnaces in the Upper Peninsula of Michigan that were used to melt down and purify iron ore.  Only two sites remain including the Bay Furnace in Christmas, and Fayette on the Garden Peninsula east of Escanaba.  Iron ore was first discovered in the U.P. in the 1840s.  Although the iron ore rock was up to 72 percent pure, it was necessary to remove the impurities and extract the iron.

Iron is purified from iron ore in a huge container called a blast furnace. Beginning in the 1840s in Michigan’s Upper Peninsula, iron ores such as hematite and magnetite were mined and then transported to blast furnaces.  To purify the ore, the rock was added to the blast furnace along with limestone and charcoal.  The mixture was heated to around 2282°F (1250°C) almost 300 degrees below iron’s melting point of 2786°F (1538°C).

In this reduction reaction, the charcoal was used to heat the mixture and add carbon to the chemical reaction.  The limestone served as a flux that helped to catalyze the desired reaction and chemically bind to and remove impurities, such as silica.  In this reaction, the iron oxide was reduced to iron, the carbon was oxidized to carbon dioxide, and the impurities were formed into glass-like slag, which was separated and removed. A picture of the Bay Furnace in its reconstructed condition is shown below.

CITES: https://en.wikipedia.org/wiki/Slag


NOTE: More Grand Marais scenes are posted often on my blog at www.agatelady.blogspot.com and on my main personal Facebook page at https://www.facebook.com/karen.brzys . I also post agate photos, shared mostly on various Facebook rockhounding sites, to the museum’s Facebook page at https://www.facebook.com/pages/Gitche-Gumee-Agate-and-History-Museum.

For this webpage update, I have selected some of my favorite pictures that I took in the Grand Marais area between July and early November of this year.

Those of you who have followed my webpage and my blog know that I love being in the right place to take photos of animals in nature. During a hike in the western part of Grand Sable Dunes, a friend of mine spotted the snowy owl shown below.


I also take many pictures of Lake Superior sunsets. One that I took late summer is below.


In early September I went on a hike with friends in the Pictured Rocks National Lakeshore. We hiked the Chapel Loop, which is around 9.4 miles long. Two photos are below.

This past two years we have seen a considerable amount of erosion on the local beaches. It is difficult now to walk west of Grand Marais to the Sable River. Also, my favorite agate hunting beach east of town is no longer accessible. A photo of the bluff is shown below.


The fierce storms and the waves that result are responsible for the erosion. A series of three photos I took of the lighthouse at the end of the breakwall document some of these waves.

This has been the warmest and most beautiful fall since I moved to Grand Marais in 1994. Below are a few of the fall photos.

Below is another fall photo of Sable Falls.


Of course, I have to include a couple fall photos of Sable Lake and one of the Grand Sable Dunes.