Ohio flint is the official gemstone of Ohio. It was designated the state stone in 1965. There are ridges and other deposits throughout Ohio, but most can be found in the eastern and central parts of the state. Flint is a microcrystalline variety of silica (quartz). It is very closely related to Jasper and … Continue reading "Mineral of the Month – Ohio Flint August 2018"
Fordite, also known as Detroit agate or Motor Agate, is not actually a rock or a mineral. However, it is used in lapidary to make amazing pieces of jewelry, some of which sell for hundreds of dollars. Fordite is actually old automobile paint which has hardened into layers. Decades ago, the process used to paint … Continue reading "MINERAL OF THE MONTH: April 2018 – Fordite"
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 … Continue reading "MINERAL OF THE MONTH: December 2017 – Septarian Nodule"
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 … Continue reading "MINERAL OF THE MONTH: July 2017 – Kona Dolomite"
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 … Continue reading "MINERAL OF THE MONTH: March 2017 – Chert"
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 … Continue reading "MINERAL OF THE MONTH: June 2016 – Lake Superior Copper Replacement Agates"
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 … Continue reading "MINERAL OF THE MONTH: November 2015 – Slag"
Okay, I will admit it. I didn’t realize until now that in this version of my webpage I have not yet featured the state stone for Michigan: the Petoskey stone. As I have changed webmasters over the last dozen years or more, the content of the webpage has also changed since I have started fresh … Continue reading "MINERAL OF THE MONTH: June 2015 – Petoskey Stone (Michigan)"
The condor agate was discovered and named by Luis de los Santos in 1993 in the Andes Patagonia Mountains near San Rafael, in Mendoza Province, Argentina. This agate exhibits vibrantly colorful bands and patterns, and has become a popular stone among collectors and jewelry designers. Close up photos of the condor agate shown above follow. … Continue reading "MINERAL OF THE MONTH: February 2015 – Condor Agate (Argentina)"
Corundum is a crystalline form of aluminum oxide (Al2O3) with traces of iron, titanium and chromium. It can be found as a component in rocks as well as in pure crystal form. It is one of the naturally transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems … Continue reading "MINERAL OF THE MONTH: September 2014 – Black Corundum"
Tiger’s eye (also called Tigers eye or Tiger eye) is an unusual quartz rock that forms when silica replaces a fibrous form of blue asbestos (crocidolite). Rocks that form under this replacement process are called pseudomorphs. It comes in various colors, but is naturally golden in color. Red tigers eye stones are manipulated with heat … Continue reading "MINERAL OF THE MONTH: April 2014 – Tiger’s Eye"
Although controversial, some people classify Skip-an-Atom Agates as s a sub-variety of Lake Superior Agate. These rocks are usually opaque with patterns of large quartz crystals with evenly distributed tiny air spaces that sometimes manifest with a lilac color cast. These Lake Superior nodules are usually found in and around Duluth, MN – and are … Continue reading "MINERAL OF THE MONTH: November 2013 – Skip-an-Atom Agate"
This rock was first discovered in the United States in the Unakas mountains of North Carolina. Unakite is an altered form of granite composed of pink orthoclase feldspar, green epidote, and quartz. The green epidote can vary in its shade of green, as can the pink feldspar. Usually the colors combine to create a mottled … Continue reading "MINERAL OF THE MONTH: August 2013 – Unakite"
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 … Continue reading "MINERAL OF THE MONTH: March 2013 – 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 … Continue reading "MINERAL OF THE MONTH: September 2012 – Chlorastrolite Greenstone"
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 … Continue reading "MINERAL OF THE MONTH: June 2012 – Moqui Marbles"
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 … Continue reading "MINERAL OF THE MONTH: March 2012 – Mexican Crazy Lace Agate"
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 … Continue reading "MINERAL OF THE MONTH: January 2012 – Mary Ellen Jasper"
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 … Continue reading "MINERAL OF THE MONTH: Winter 2011 – Argentina Condor Agate"
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 … Continue reading "MINERAL OF THE MONTH: September 2011 – Petoskey Stones"
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 … Continue reading "MINERAL OF THE MONTH: Spring 2011 – Petrified Wood"
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 … Continue reading "MINERAL OF THE MONTH: Fall 2010 – Ammonite Fossil"
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 … Continue reading "MINERAL OF THE MONTH: August and September 2010 – Polyhedroid Agate"
Mookaite jasper is a sedimentary rock formed when ancient sea bed sediment was jasperized into a mottled and beautiful quartz rock. This decorative rock, which is often used in jewelry, has truly beautiful patterns. It is only found in Australia and has the same earthy colors as those used by Aborigines in their art work. … Continue reading "MINERAL OF THE MONTH: July 2010 – Mookaite Jasper"
A meteorite is a piece of a meteor that reaches the earth’s surface. Most of the meteorites found today were not witnessed when they fell. The Nantan meteorite fall is an exception. In May of 1516 during the reign of the Chinese Emperor Zhengde, the meteor hit the atmosphere above the Nantan province of … Continue reading "MINERAL OF THE MONTH: June 2010 – Nantan Meteorite"
The mineral of the month is Kentucky agate. It became the state stone for Kentucky in 2000. This agate is quite unique in its coloration. It most typically has bands of yellow, black, and gray. Occasionally there are sections of blue, red, pink, or orange. This distinctive agate was formed in shale and siltstone in … Continue reading "MINERAL OF THE MONTH: April/May 2010 – Kentucky Agate"
This month’s featured mineral is fossilized dinosaur bone. For the new agate book, Tom Shearer borrowed samples of fossilized bone from Mark Anderson (www.differentseasonsjewelry.com). The specimens pictured below come from Utah. Although they certainly have agate pockets, technically the fossilization process is different than the agatization process. Therefore, these specimens are classified as fossilized dinosaur … Continue reading "MINERAL OF THE MONTH: March 2010 – Fossilized Dinosaur Bone"
The Fairburn Agate is the state stone in South Dakota. It is named after the town from which the first agates were found: Fairburn, SD. This is an unusual agate, in that they formed in sedimentary rock, rather than igneous rock in which most other agates formed. This sedimentary genesis probably contributed the minerals which … Continue reading "MINERAL OF THE MONTH: Fall 2009 – Fairburn Agate"
In the iron-rich areas around Lake Superior, there are deposits of banded iron formation. In addition to being called banded iron formation, many rockhounds label specimens as Jasperite, Jaspite, or Jaspelite. This is a distinctive type of rock found in Precambrian sedimentary rocks. The structures consist of repeated layers of iron oxides, either magnetite or … Continue reading "MINERAL OF THE MONTH: September 2009 – Banded Iron Formation"
Goethite (pronounced: “Gertite”) forms by the oxidation of iron-rich deposits. It was named after the German multi-disciplinarian Johann Wolfgang von Goethe. It usually occurs as massive, botryoidal or stalactitic formations and tends to be found in soil and other low-temperature environments. It is in the hydroxide group with a hardness of 5 to 5 ½ … Continue reading "MINERAL OF THE MONTH: August 2009 – Goethite"
Obsidian is a dark volcanic glass. It is rich in silica and breaks with a very sharp conchoidal fracture. It is formed by the very rapid cooling of viscous acid lava. Although black is the most common color, it is also found in a variety of other colors from mahogany to red, green, pink, blue, … Continue reading "MINERAL OF THE MONTH: July 2009 – Obsidian Needles"
Coyamito Agate from Chihuahua, Mexico The mineral of the month is the Coyamito Agate from northern Mexico. It is mined on a ranch located around 40 miles from the world famous Laguna Agate location, which is around 75 miles south of El Paso, Texas. The ranch is in the middle of the Chihuahuan desert at … Continue reading "MINERAL OF THE MONTH: Spring 2009"
Several different minerals form into rosette shapes including chalcedony, aragonite, hematite, barite, and selenite (a form of gypsum). This month’s mineral is the selenite “Desert Rose.” It is most similar to barite roses, but its edges are sharper and the crystalline structure is less hard. Thus, Desert Roses are brittle and can break quite … Continue reading "MINERAL OF THE MONTH: March 2009 Selenite Desert Rose"
A new, but very small deposit of Polychrome Jasper has recently been found in the deserts of Madagascar. Specimens from this deposit were first sold at the Denver Gem and Mineral Show last September. Since I was going to the Tucson Show, I was commissioned to purchase larger and unusual mineral art specimens from … Continue reading "MINERAL OF THE MONTH: February 2009 Polychrome Jasper"
The featured mineral this month is what I call Sea Shell Jasper. Others call it Shell Jasper, or Shell Marble Jasper. It is a new mineral that comes from China. Although it is marketed as jasper, it is actually marble. It has beautiful mottled black, white, and gray colored patterns that appear as a conglomerate … Continue reading "MINERAL OF THE MONTH: January 2009 Sea Shell Jasper"
Jasper is a form of microcrystaline quartz. Its name comes from the Greek word, iaspis, which means “Spotted Stone.” Jasper comes in many colors and patterns, but is most often red, brown, or green. Jasper is what I refer to as a “First Cousin” to agate. Both semiprecious stones are microcrystaline quartz. The difference … Continue reading "MINERAL OF THE MONTH: December 2008 Picture Jasper"
This yellow-green mineral is found throughout the world, but most notably in Australia, South Africa, Germany, and the United States. The specimen featured this month was found in the Keeweenaw Peninsula in Michigan’s Upper Peninsula. It not only includes crystals of Prehnite, but also specs of copper, calcite, and silver. It forms near the surface … Continue reading "MINERAL OF THE MONTH: November 2008 Prehnite"
Mexican Opal comes from the Magdalena, Jalisco area of Mexico. Historians have determined that the Aztec people used Mexican opal for ceremonial and ornamental purposes between 1200 and the early 1500s when the Spaniards Conquistadors took over the area. It is known by locals as vitzitziltecpal or the “humming bird stone” due to the iridescent … Continue reading "MINERAL OF THE MONTH: October 2008 Mexican Opal"
Technically “Mohawkite” is not a mineral but is a combination of copper arsenates with nickel and cobalt. It is also considered a variety of Domeykite. It is named after the original locality: the Mohawk Mine located in the Keeweenaw Peninsula of Michigan’s Upper Peninsula. This is the only location in the world that Mohawkite is … Continue reading "MINERAL OF THE MONTH: September 2008 Mohawkite"
The mineral of the month for the summer 2008 update is Marra Mamba Tiger’s Eye. This mineral is found in western Australia, near Mount Brockman, but is thought to have been mined out over a decade ago. It forms when silica quartz replaces crocidolite (asbestiform riebeckite). Marra Mamba tiger’s Eye is known for its quality … Continue reading "MINERAL OF THE MONTH: Summer 2008 Marra Mamba Tiger’s Eye"
At the request of a customer, I am going to again feature Ocean Jasper as the Mineral of the Month. Ocean Jasper made an appearance on the original web page several years ago, but it deserves to come back. Until I completed an Internet search about Ocean Jasper while preparing this web page update, I … Continue reading "MINERAL OF THE MONTH: June 2008 Ocean Jasper"
The mineral of the month for May 2008 is Apophylite. This specimen was acquired from a Brazilian dealer who was liquefying his entire inventory at the Tucson show a couple of years ago. He said something about wanting to go fishing. Apophyllite is in the Silicate class of minerals, which tend to be translucent and … Continue reading "MINERAL OF THE MONTH: May 2008 Apophylite"
The mineral of the month is my favorite agate: the shadow agate. This specimen was picked up off the Grand Marais beach by the museum founder, Axel Niemi. He found it in 1925 when he was just eight years old. He had it for almost 40 years when he finally sliced the agate, discovering the … Continue reading "MINERAL OF THE MONTH: April 2008 Shadow Agate"
It has been quite some time since I designated the Lake Superior Agate as the mineral of the month. In honor of the museum founder, I am featuring his 5.5 agate as the mineral of the month. He found this agate at the base of Grand Sable Dunes in 1958. He had it for many … Continue reading "MINERAL OF THE MONTH: March 2008 Lake Superior Agate"
Amazonite, sometimes called Amazonstone, is a layered form of microcline feldspar; it was originally named after the Amazon River when similar green stones were found there. However, no deposits of Amazonite have ever been found near the Amazon River. Amazonite is a rare mineral. Originally, it was obtained from the Limen Mountains in Russia. More … Continue reading "MINERAL OF THE MONTH: February 2008 Amazonite"
January’s mineral of the month is native copper. This interesting specimen was recently donated to the museum by Peter Pagel, from Marquette. He acquired it from the Houghton area. It is a thick slab of native copper in matrix that is 7 inches by 6 inches. This specimen was mined from the Keweenaw Peninsula, which … Continue reading "MINERAL OF THE MONTH: January 2008 Native Copper"
In keeping with the latest web page effort to provide information about the Lake Superior basin, this month’s Mineral of the Month is Nepheline Syenite. Nephelene syenite is an igneous rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, … Continue reading "MINERAL OF THE MONTH: December 2007 Nepheline Syenite"
Recently, the museum was able to purchase some incredible museum-quality Malachite specimens to sell in the gift shop. One is pictured below. Malachite is a copper carbonate hydroxide mineral. It forms in botryoidal, fibrous, or stalagmitic masses, usually from the weathering of copper ores. The stone’s name derives from the Greek word, molochitis, which means … Continue reading "MINERAL OF THE MONTH: Fall 2007 Malachite"
This month’s featured mineral is Rain Flower Agate from Nanijing, China. For those of you who periodically check which Lake Superior agates are listed on Ebay, you have seen the listings for these “Lake Superior-Like” agates. Rain Flower agates are river washed to a smooth surface featuring translucent, rich, banding patterns. They are found … Continue reading "MINERAL OF THE MONTH: August 2007 Rain Flower Agate"
This month’s mineral of the month is Labradorite, which was first discovered in the Labrador Peninsula in Canada. It is also found in Norway, Finland, and Russia. It is truly a captivating mineral that displays a colorful shiller effect when held and moved during observation. The color display is from layers of intergrowth inside the … Continue reading "MINERAL OF THE MONTH: July 2007: Labadorite"
The mineral of the month is a Lake Superior Michipicoten agate. When a newspaper article was published in 1958 featuring the museum founder, Axel Niemi, and his 5.5-pound agate, Axel received a letter from Mrs. J. Oldenkomp. She had seen the article and asked Axel if he was interested in buying an agate that she … Continue reading "MINERAL OF THE MONTH: June 2007: Lake Superior Michipicoten Agate"
This month the featured mineral is Rainbow Fluorite. Fluorite is a derivative of the Latin word “fluere” which means to flow. Because of its easy melting properties, fluorite can be used during the manufacturing of steel; although its most popular use is in making jewelry. This is because fluorite is the most colorful mineral of … Continue reading "MINERAL OF THE MONTH: May 2007: Rainbow Fluorite"