Michigan Stones – Petoskey Stone, Greenstone, and More !
Written by Linda Michaels
Petoskey Stone is Michigan’s State Stone: Hexagonaria Percarinata, has a hardness 3.0, and is a fossil colonial coral found throughout the northern portions of Lower Michigan, and is a variety of calcite.
Greenstone or Chlorastrolite is Michigan’s State Gem. Hardness is 5.5 and is found on the Keweenaw Peninsula of Western Upper Michigan and on Isle Royale in Lake Superior.
Copper-Native Element. Hardness 2.5-3.0. Native copper in pure metal form is rare. The Keweenaw Peninsula of Michigan is the world’s most important source.
Sulfur A Native Element. Hardness 1.5-2.5. This element is found in Monroe County of Lower Michigan. Primarily as crystals or masses in vugs (a cavity or hollow in a rock, often lined with crystals.) in limestone.
Amethyst has a hardness of 7. A rare gemstone found near Copper Harbor, Keweenaw Peninsula. This purple variety of quartz is found here.
Halite or Salt has a hardness of 2. Cubic shaped crystals formed by evaporation. Large deposits of this mineral occur in Wayne County, southeastern Lower Michigan.
Pyrite or “Fools Gold” has a hardness of 6.0-6.5. Pale yellow in color and is confused with gold, so called, “Fools Gold” is found throughout Michigan and is the most common iron sulfide.
Hematite hardness is 5-6 and is abundant iron ore mineral found throughout the Upper Peninsula. This variety is called Specular Hematite.
Pudding Stone Pudding Stone is a conglomerate rock made up of a mixture of different, irregular sized grains and pebbles held together by a finer matrix, usually formed from quartz sand. The pebbles are Jasper and the matrix is Calcite.
Leland Blue This Glass slag is from the pig iron factory in Leland, Michigan. Charcoal from local hardwoods was made in large “beehive” furnaces and burned with limestone flux to separate the iron. The byproduct was a glassy slag in unique variety of blue, green and purple colors.
Verde Marble is a Serpentine Marble. The mineral [magnesium hydroxy silicate] is found in a quarry located in Ishpeming, Michigan. It is a deep green crossed by veins and dots of lighter green, almost a dark army green color and white.
Horn Coral – Ruyossa, which means wrinkled. It grows in a long cone shape, like a bull’s horn and was native to the Emmet County area.
Chain Coral is a Colonial coral. Chain coral is over 400 million years old. Chain Coral lived during the Silurian Period in what is now Lake Michigan. The chains in the Chain coral are made up of white quartz. Each link in the chain was where an individual animal lived. As this fossil coral is made up of many individual coral animals and is known as a colonial coral.
Favosite coral is a cousin to Petoskey stone. It is a coral composed of marine animals which are polygonal to slightly rounded in shape. When Michigan was closer to the equator they grew in the shallow tropical waters some 350 million years ago. The closely adjoined colonies give the formation a honeycomb-like appearance and are very hard to find. Favosite is also known as Charlevoix stone and is a tabulate coral.
Lake Superior beach stones are opaque stones found on the beaches of Lake Superior. They were formed from volcanic lava that quickly cooled when it reached the surface. Some of them contain tiny crystals, Jasper, Iron with a mix of Silica and other colorful minerals.
Prehnite is a yellow green mineral found throughout the world, but most notably in Austrialia, South Africa, Germany, and the United States in the Keweenaw Peninsula in Upper Michigan. Prehnite can have specks of copper, calcite, and silver, and it forms near the surface of basaltic lava flows and often occurs in geodes or veins. It forms as a result of low grade metamorphism from hydrothermal solutions. Prehnite can be confused with Gryrolite, Smithsonite, or Hemimorphite. Prehnite minerals in Smithsonite have more of the vitreous or pearly luster and Hemimorphite is usually bluer in color while Gyrolit is not as glassy. Prehnite is a phyllosilicate of calcium and aluminum. It is brittle with an uneven fracture and a slight vitreous luster with a white streak. It has a hardness of 6 to 6.5, with an average specific gravity of 2.80-2.90. It is translucent with a color that varies from light green to grey, yellow, or white. When heated, this mineral gives up water but will not take the water back up when cooled. Phrenite was first discovered in South Africa by Colonel Hendrik Von Prehn, an early Dutch governor of the Cape of Good Hope colony. It was the first mineral to be named after a person. Prehnite’s metaphysical properties are thought to enhance energy, provide protection, and promote calmness. It is also used to advance the state of meditation and help you to remember.
Kona Dolamite All rocks are old, right? True, but some are much older than others! This isa pink Dolomite, one of the oldest on the planet. Dolomite is an ancient rock in which formations of fossilized algae occur. The algae in these beautiful semi-precious stones began as some of the first life on earth ! Each specimen of rock is a minimum of 2.2 billion years old. This is older than diamonds and half as old as the planet itself. This sublime specimen, Kona Dolamite, comes from Michigan’s Upper Peninsula. It is named for the Kona Hills south of Marquette and is mined here. These fossil formations are found in the lower eras of the Middle Precambrian Period. Kona Dolamite is found in a variety of colors: brown, yellow, cream, red, pink, and orange, with shades of brown, cream, and gray. The stone usually has black mottling, banding, or lacing. Pink or salmon with the black bands are the most desirable
Thomsonite was created from lava flows of the Keweenawan Period, over 600 million years ago. Gases within the lava seams between the lava flows turned into hollow pockets when the lava hardened. Over hundreds of thousands of years, these hollow openings filled and solidified, forming Thomsonite. The unique combination of volcanic activity and certain chemicals and minerals is responsible for why the gemstone formed in this location along the North Shore. Thomsonite is found in the Kilpatrick Hills of Scotland; in the north of Ireland; Saxony, Germany; the Faroe Islands; Kern County, Califorinia; Cape Lookout, Oregon; and in the Lake Superior region. It can also be found on beaches between Tofte and Grand Marais, on the Coo-Lake County line, on Island Royal, Michigan and near Saxon Falls and the Montreal River Gorge on the Keweenaw Peninsula in Michigan. The color and texture of Minnesota’s Thomsonite makes it unique as gem-quality, stones are found only in a limited area of Lake Superior’s shoreline about 5.5 miles southwest of Grand Marais. Being a rare mineral, belonging to the zeolite group of minerals, which has over 35 different recognized members. Thomsonite is one of the rarer zeolites. It forms tight acicular radiating clusters and sphericules as well as some blockier crystals and is found in the vesicles or bubbles of volcanic rock, as are most other zeolites. Dr. Thomas Thomson, first described the mineral in 1840. Thomson discovered it in the Kilpatrick Hills of Scotland, and Thomsonite has been named after him. The Minnesota Geological Survey was established in 1873 and headed by Newton Winchell, who taught in the winter and conducted surveys in the summer. Two of his students, young professors from the University of Minnesota, S.F. Peckman and C.W. Hall, spent their vacation in 1879 along thew north shore of Lake Superior studying rocks. A report they published in 1888 is the first printed reference to Thomsonite. Pure Thomsonite is snow-white and sometimes translucent. Other compounds such as ferric and or ferrous iron or copper are responsible for the variouscolorations within the gemstone. Commonly found colors are pink, tan, white, red and brown. Thomsonite has green, gray, black or green eyes. Green eyes are the most highly prized and least found. Thomsonite specimens are usually small. A little finger nail sized stone with a good radiating pattern can be considered a nice specimen. Look for white, chalky, small round or almond shaped nodules in Thomsonite. Thomsonite is also called: Eyestone [eye agate] or Lintonite which is an agate like variety of Thomsonite with alternating bands of pinkish and green, that appear eye like. This name is applied in particular to pieces with green zones in them and from the Lake Superior region of Michigan and Minnesota.
Lake Superior Agates are the oldest on Earth. Lake Superior Agates have a hardness of 7.0. They formed in the late Precambrian period almost 1.2 billion years ago. Only 1 in every 10,000 specimens are good enough for jewelry. They are found throughout the northern United States having been spread to the original Lake Superior region by glaciation. They can be found throughout upper Michigan in glacial tills and many Lake Superior beaches. It is usually pale in coloring, red, orange or yellow. The color scheme is caused by the oxidation of iron. Iron leached from rocks provided the pigment that gives the gemstone its array of color. The concentration of iron and the amount of oxidation determine the color within or between an agate’s bands. A banded pattern, the fortification agate, is the most common Lake Superior agate. Its bands, or “face”, connect to each other like the walls of a fort, which is where the name came from. Sub-types of fortification agate are the parallel-banded, onyx-fortification or water-level agate. These stones have straight parallel bands all over or over part of them. Their size can be pea size up to 20 lbs! The large size is rare . The most popular Lake Superior agate is one of the rarest which is one that has the eye with perfectly round bands or “eyes” dotting the surface. Water washed agates are sometimes found, but rare, with a smooth surface from being battered from the waves. Lake Superior Agates are a colorful form of Chalcedony and are said to enhance creativity. A book written by Scott F. Wolter, “The Lake Superior Agate” and “The Lake Superior Agate- One Mans Journey” are great sources of information.