Category: Mineral of the Month

Jacobsville Sandstone is a red sandstone that has light-colored streaks and spots caused by chemical leaching across the bedding planes. This beautiful rock is found along the Lake Superior shoreline in northern Upper Michigan and Ontario. Scientists also think that Jacobsville lies under much of Lake Superior. There are also other sandstones in Wisconsin and Minnesota that may or may not be the same formation (Freda sandstone, Bayfield Group sandstone). Jacobsville Sandstone is composed of: 27.4% nonundulatory quartz, 27.0% undulatory quartz, 23.0% potassium feldspar, and 12.3% silicic volcanic clasts.

Below is a table showing the sandstone sales from 1899 to 1913.

Year	Total Value
1899	$178,038
1900	$132,650
1901	$174,428
1902	$188,073
1903	$121,350
1904	$74,868
1905	$123,123
1906	$65,395
1907	$53,003
1908	$39,103
1909	$36,084
1910	$31,233
1911	$12,985
1912	$16,438
1913	$19,224

There is some confusion about this rock since it has had several names including redstone, brownstone, Lake Superior Sandstone, and Eastern Sandstone. In 1907, however, the sedimentary formation was given its current classification and the name Jacobsville, in honor of the town in which some of the quarries were located. There is also disagreement about the age of the sandstone. Most believe that it formed around a billion years ago, but others feel that it is half that age. Since the sandstone is entirely devoid of fossils, the older age classification is more likely.

Today, the best place to see this rock is near Au Sable Point, located around eight miles west of Grand Marais.

CITES:

• http://en.wikipedia.org/wiki/Jacobsville_Sandstone

The mineral of the month is Chlorastrolite, also known as Isle Royale greenstone. This mineral was designated as the official state gem by Michigan’s 76th Legislature (Act 56, PA 1972). This legislation was introduced by Representative Russell Hellman of Dollar Bay. This mineral is a green variety of the mineral pumpellyite, and has a pattern of star-like crystals which forms a turtle-shell pattern. Greenstones are found in the waters and on the shores of Isle Royale, where it is illegal to collect due to the island’s national park status. It can also be found in the Michigan Copper ranges in the western Upper Peninsula. Many of the old tailings left over from the mining era have greenstones in them. They appear as dark green, small round or almond shape nodules in the basaltic rock. In some cases these nodules have weathered out of the volcanic rock and can be found along the shoreline. Unfortunately, only a small percentage of the green nodules are actual greenstones, as most are chloride, prehnite or some other mix of minerals. And of course, of all the greenstones found, perhaps only a few out of every hundred are gem quality.

It is difficult to identify an unpolished pebble of chlorastrolite. Most gem quality greenstones are very small, and it is rare to find one that is larger than a half inch. The largest gem quality stone is in the Smithsonian and measures 1.5 by 3 inches.

Since it is illegal to search for these gemstones on Isle Royal, the best localities now are the waste rock piles located in the old Keweenaw Peninsula mines in the western Upper Peninsula of Michigan. Some possible search sites include the Central, Central Exploration, Cliff, Phoenix, Mandan, and Delaware mines as well as some of the shoreline outcrops near Eagle Harbor.

 

The mineral of the month for this update is an unusual type of iron concretion called Moqui Marbles. These round rocks form in the Navajo Sandstone formations spread across northern Arizona, northwest Colorado, and Utah. Most are found in the numerous national parks in the area, so they can no longer be collected. I recently purchased a large quantity of moqui marbles that were collected legally many decades ago.

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The wide range of colors exhibited by the Navajo Sandstone reflect alteration by groundwater fluids over the last 190 million years. The different colors are caused by the presence of varying mixtures and amounts of iron minerals such as hematite, goethite, and limonite. These minerals fill the pore spaces between grains of sand, causing the variation in colors in the sedimentary layers. The iron in these strata originally arrived via the erosion of iron-bearing silicate minerals. Variations in the type and proportions of precipitated iron oxides resulted in the different crimson, vermillion, orange, salmon, peach, pink, gold, and yellow colors of the Navajo Sandstone.

The Navajo Sandstone is also well known for its iron concretions. They are believed to represent an extension of Hopi Native American traditions regarding ancestor worship (“moqui” translates to “the dead” in the Hopi language). Informally, they are called “Moqui marbles” after the local proposed Moqui native American tribe. Thousands of these concretions weather out of outcrops of the Navajo Sandstone within south-central and southeastern Utah within an area extending from Zion National Park eastward to Arches and Canyonland national parks. They are quite abundant within Grand Staircase-Escalante National Monument. The Utah concretions formed around 25 million years ago when minerals precipitated from groundwater flowing through much older Navajo sandstone.

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The iron oxide concretions found in the Navajo Sandstone exhibit a wide variety of sizes and shapes including discs, buttons, spiked balls, hollow pipes, round spheres, and others. Although many of these concretions are fused together like soap bubbles, many more also occur as isolated concretions, which range in diameter from the size of peas to baseballs.

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These concretions are regarded as terrestrial analogues of the hematite spherules, called Martian “blueberries” or more technically Martian spherules, which the Opportunity Rover found on Mars.

Many people like to buy Moqui Marbles in pairs. The “male” spheres have ridges whereas the “female” spheres are smoother. Used together they balance the masculine and feminine energies. They are believed to be among the most energetic stones on earth. Their major properties are claimed to be cleansing, relaxation, and they provide a great boost to meditation.

The mineral of the month for this update is Mexican Crazy Lace agate. Crazy lace agate, also known as Mexican agate, is an attractive, multi-colored agate that is patterned like a beautiful, multicolored paisley cloth. It is found in Northern Mexico in the state of Chihuahua. This is the largest of the 31 Mexican states – slightly larger than Great Britain.

Although Mexican agates were first documented in 1895, it wasn’t until some 50 years later that a few American rockhounds found a few small agates not far from the newly constructed highway they were travelling between Ciudad Juárez and Ciudad Chihuahua. Many different types of agates are found in this region, mostly in isolated deposits within andesites, rhyolites, and ash flow tuffs that range in age from 38 to 44 million years old. The only exception is Mexican Crazy Lace Agate which is uniquely found in a limestone layer of Cretaceous age (90 to 65 million years old). The Crazy Lace deposit is located southwest of Villa Ahumada.

In ancient times, this agate was worn to placate the gods, and to give courage. It will improve eyesight, illuminate your mind, allow you to be more eloquent, and give vitality. It keeps the wearer well-balanced, focused, and improves ability to accomplish goals and overcome adversity. Like other agates and silica rocks, Crazy Lace agate is a good general healing stone.

 

The mineral of the month for this update is Mary Ellen Jasper. Unless you live in Minnesota, you may not be familiar with this interesting form of microcrystalline quartz. This rock formed more than two billion years ago in the area that is now the Mesabi Iron Range in Northern, Minnesota. At that time one of the early life forms evolved in the ancient seas. These blue-green single-celled cyanobacteria contained chlorophyll and were able to harvest the energy of the sun to photosynthesize and produce their own food. Energy from sunlight was used to split carbon dioxide into carbon and oxygen. The carbon was absorbed, becoming part of the growing organism, and the oxygen was released into the atmosphere. Prior to the evolution of cyanobacteria, there was almost no oxygen in the atmosphere. Once these organisms developed, they proliferated and helped to trigger drastic changes in the earth’s atmosphere, climate, and environment.

Some of the cyanobacteria lived in colonies that produced macro-scale structures called stromatolites. A drawing depicting what a stromatolite shoreline may have looked like during the latter part of the Archean period is shown below. Evidence of fossil stromatolite formations have been found throughout the world so these mushroom-shaped mounds dominated the shores of all the newly developing landmasses, including the area where the Mary Ellen Jasper developed.

The earliest stromatolite of confirmed origin dates to 2,724 million years ago. A recent discovery, however, provides strong evidence that microbial stromatolites extending as far back as 3,450 million years ago. These organisms were extremely resilient and adaptable, allowing them to be a major constituent of the fossil record for the first 3,500 million years of life on earth, with their abundance peaking about 1,250 million years ago.

Until the mid-1950s, scientists thought that stromatolites were long since extinct. That all changed in 1956 when living stromatolites were found in the Hamlin Pool located on the south end of Sharks Bay in Western Australia. Since then, live stromatolites have also been found in several sites in the Bahamas. Pictures of both are included below.

Stromatolites are stony structures built up by algae and cyanobacteria. The microbes live in gooey mats on the top surface of the structures. These mats trap fine sediments carried across them by tidal currents. As the mats fill in with sediments and become opaque, the microbes move upwards seeking sunlight. Stromatolites differ from normal fossils because they are formed by the activities of micro-organisms. They result from a combination of trapping, binding and precipitation of sediment.

One of the biggest impacts that stromatolites had on the earth was the release of free oxygen, which was a byproduct of their photosynthesis. When stromatolites first evolved, the earth’s atmosphere had less than one percent oxygen. After the stromatolites evolved, significant amounts of oxygen did not accumulate in the atmosphere right away because of the vast quantities of oxidizable materials in the earth’s crust as well as the dissolved eager-to-combine iron in the oceans. For more than a hundred million years, these materials absorbed any free oxygen that was produced. Mary Ellen Jasper developed not only from the remains of the stromatolites, but also from the oxidization of iron that was present in the area that is now northern Minnesota.

A few more pictures of Mary Ellen Jasper are included below. The first two pictures are of a thin polished slab. The first is displayed with front lighting and the second with back lighting.

Coincidently, I just polished a piece of Mary Ellen Jasper for a customer a couple of days ago. Here is a picture of that specimen.

During the past several years Argentina has become one of the new hot beds for agate prospecting. The condor agate was introduced to the U.S. market in 1992 by the former Argentinean actor, Luis de los Santos. Since then he discovered the puma agate in 1993, the crater agate in 1997, and more recently the Black River agate. Prospecting and mining these agates is difficult. Not only are the locations extremely remote, but the work must be done at elevation where the weather is often not cooperative. Luis named this agate after the large Condor birds that were flying over him during the trip that he discovered the agate. It is mined at over 6,000 feet. The site can only be reached by horse back.

 

In 1965 the state stone for Michigan was designated as the Petoskey stone. Petoskey stones are fossils of coral colonies called Hexagonaria. “Hex” comes from hexagon, because the coral is usually a six-sided polygon. The coral grew 350 million years ago, 150 million years before the dinosaurs! It grew only in shallow tropical salt-water seas where lower Michigan is now. The coral stacked in layers, then fossilized into rock.

The Petoskey stones found on the beaches of Lakes Michigan and Huron were formed as a result of glaciation, in which sheets of ice plucked stones from the bedrock, grinding off their rough edges and depositing them primarily in the northern portion of Michigan’s Lower Peninsula. In some areas of Michigan, complete fossilized coral colony heads can be found. The formations and specimens found inland tend to be rougher since they have not been weathered as much by the wind, water, and sand from the shoreline. The movement of the frozen lake ice acting on the shore during the winters is thought to turn over stones at the shore exposing new Petoskey stones at the water’s edge each spring.

Similar fossil corals occur in a variety of locations; however the name Petoskey stone should only be applied to those from Michigan which exhibit a six-walled coral structure that has the distinctive “eye” pattern within each cell.

When ancient glaciers pressed down on the center of the Lower Peninsula, the layer of fossilized coral rose up to form a ridge and created the dish shaped “Michigan basin”. The exposed layer of rock is where Petoskey stones come from. Petoskey stones are found in the Gravel Point Formation of the Traverse Group. They are fragments of a coral reef that was originally deposited during the Devonian period. When dry, the stone resembles ordinary limestone but when wet or polished using lapidary techniques, the distinctive mottled pattern of the six-sided coral fossils emerges.

It is sometimes made into decorative objects. Other forms of fossilized coral are also found in the same location including the closely related favorites. Favosites is an extinct genus of coral characterized by polygonal closely-packed corallites (giving it the common name “honeycomb coral”). The walls between corallites are pierced by pores which allowed transfer of nutrients between polyps.

The name comes from an Ottawa Indian Chief, Chief Petosegay. The city of Petoskey, Michigan, is also named after him, and is the center of the area where the stones are found. According to legend, Petosegay was the child of a descendant of French nobleman and fur trader, Antoine Carre and an Ottawa princess. Petosegay, meaning “rising sun”, “rays of dawn” or “sunbeams of promise”, was named after the rays of sun that fell upon his newborn face. In keeping with his promising name, Petosegay was a wealthy fur trader who gained much land and acclaim for himself and his tribe. He was remarked upon to have a striking and appealing appearance, and spoke English very well. He married another Ottawa, and together they had two daughters and eight sons. In the summer of 1873, a few years before the chief’s passing, a city began on his land along Little Traverse Bay. The settlers christened the newborn city Petoskey, an anglicized form of Petosegay.

 

Petrified Wood can be thought of as a type of fossil. Fossils are formed from a petrification process, which is a geology term describing the method by which organic living material is converted into stone. Usually, this happens when the organic remains are buried in lava or sediments before they can decay. Petrification can take place in two related ways: replacement and permineralization. Replacement occurs when water dissolves the original hard parts and replaces them with mineral matter. The most common replacement minerals are calcite, silica, pyrite, and hematite. When the original organism is replaced quickly, the fossil usually loses the detailed structure, leaving behind just the original shape. Permineralization occurs when ground water carrying dissolved minerals infiltrates the microscopic pores. The minerals in this case replace the detail of the original organism.

The most famous example of petrification is the Petrified Forest in northern Arizona. However, this is not the only area known for petrified wood since it is also found in nearly every state and in many foreign countries. It is not known for certain who the first Europeans were to see the great display of petrified wood in Arizona. It was probably Spanish explorers during their expeditions in the 1500s. The earliest written record, however, dates from 1851 when an army officer mentioned petrified wood in a report.

At one time the northeast part of Arizona was lowland with numerous rivers and streams. In the basin there was a lush forest with conifer trees up to nine feet in diameter and over 200 feet tall. During the Triassic Period (200 to 250 million years ago), the area that is now Arizona was located near the equator. At that time, all of the continents had combined to form one super-continent called Pangea. Over time, trees in the area died. Rivers deposited the deceased trees in their flood plains or buried them in streambeds. Most of the trees decomposed, but a few were buried so deep that there was not enough oxygen to allow decay. To the west of this area were massive volcanoes that spewed ash into the atmosphere. Wind currents carried the ash and deposited it with the silt that buried the trees. Ground water dissolved silica from the ash and carried it into the buried logs. Over time, the silica in solution either replaced cell walls, crystallizing as quartz, or deposited in the air spaces within the wood tissue. This petrification process explains how cell structure, annual rings, and other features of the original trees were preserved.

As the petrification process continued, other minerals combined with quartz to create the brilliant rainbow of colors often found in petrified wood. In some cases minerals infiltrated later during the millions of years of burial as a secondary deposit in the cracks, checks, or other openings in the petrified or partially petrified wood. Iron oxides produced the great variety of shades of red, brown, and yellow. The black color was probably due to manganese oxide or carbon.

At first, the now petrified trees remained buried under 3,000 feet of sediment. However, around 60 million years ago this area was uplifted along with the Rocky Mountains. With the uplifting came erosion from streams and rivers that removed the overburden layers, exposing the petrified trees.

Some scientists classify petrified wood as agate; others do not. The determination comes down to two issues. First, the type of quartz needs to be identified. In some cases, most of the quartz in petrified wood is macrocrystalline, although there may also be some microcrystalline replacement. For those specimens that contain mostly microcrystalline crystals, the second issue is whether petrification was a replacement process, or whether it may have involved an agatization process. If the wood tissue was directly replaced by silica so that the wood fibers defined the structure, then petrified wood is not agate. If, on the other hand, each of the individual pore spaces self-organized and filled independently, thus creating individual agatized pockets, you could then classify petrified wood as a colony of agates. Depending on the specimen, there could be some of both structures.

 

The mineral of the month is the ammonite (Ammonoid) fossil. Ammonites are an extinct group of marine invertebrate animals from the Cephalopod class. These fossilized mollusks are more closely related to living cephalopods such as octopuses and squid, than they are to the modern nautilus, which has a similarly shaped shell. Two pictures of ammonite fossils are below. I took the first photo and Tom Shearer took the other two photos (Figures 135 & 136 in the new agate book).

Ammonites are excellent index fossils. Depending on the species of ammonite found in a rock layer, geologists can specify the geologic time period for that layer.

The name ammonite was inspired by the spiral shape of the fossilized shells, which somewhat resemble tightly-coiled rams’ horns. The Egyptian god, Ammon, was typically depicted wearing rams’ horns.

Eight different orders of ammonites are known to have existed, ranging from 400 million to 65.5 million years ago. They ranged in size from a fraction of an inch to over 7 feet in diameter. After being born, they fed on plankton and quickly assumed a strong protective outer shell. They also grew quickly with the females growing up to 400 percent larger than the males because they needed the extra space for egg production.

Because ammonites are extinct, little is known about their way of life. Their soft body parts were very rarely preserved in any detail. It is thought that depending on the species, they lived in a variety of ocean environments. Some probably lived in open water, while others survived at the bottom of the ocean. It is also believed that ammonites may have avoided becoming a predator’s dinner by squirting ink, much like modern cephalopods.

The soft body of the organism occupied the largest segment of the shell at the end of the coil. The smaller sections were walled off which allowed the animal to maintain its buoyancy by either filling the chambers with gas, or emptying the sea water out of these chambers. Thus the smaller sections of the coil would have floated above the larger sections. As it grew, it added newer and larger chambers to the open end of the coil.

In medieval Europe, fossil ammonites were thought to be petrified coiled snakes. These fossils were often called “snakestones” or “serpentstones.”

The mineral of the month for August/September is the Polyhedroid Agate. The unique polyhedroids are strange looking agates with geometric shapes that have smooth flat sides. Their shape appears more angular than the typical almond-shaped agate, but there is no consistency to the angles of formation. Most are either triangular or trapezoid and hollow, with the bands running parallel to their shape. Although no one knows for sure how these agates formed, there are at least two theories. Some believe that polyhedroid agates are pseudomorph replacements of other, more angular crystals. Another hypothesis is that they formed in spaces between other crystals, perhaps calcite. Unlike the rest of the Brazilian agates found in the southern part of the country, these unusual agates are found at a single site in the northern state of Paraiba. There has been no mining of polyhedroids in recent years. Most were mined during the 1970s. Believe it or not, a few polyhedroids have also been found in the Lake Superior region and in Wyoming.