Michigan Stones - Petoskey Stone, Greenstone, and More! PDF Print E-mail
Written by Linda Michaels   
Saturday, 02 May 2009 14:58



Petoskey stone- Michigan's State Stone. Hexagonaria, Hardness 3.0 A fossil colonial coral found throughout the northern portions of Lower Michigan. Variety of calcite.

Greenstone-Michigan's State Gem. Chlorastrolite. Hardness 5.5. Found on the Keweenaw Peninsula of
Western Upper Michigan and on Isle Royale in Lake Superior.

Silver- Native Element. Hardness 2.5-3.0. Native silver is found in association with the native copper deposits of the Keweenaw Peninsula of Upper Michigan.

Lake Superior Agate-Variety of Quartz. Hardness 7.0. These agates are mainly banded, a colorful form of chalcedony. Found throughout Upper Michigan in glacial tills and on many Lake Superior beaches.

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- 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 hollo

w in a rock, often lined with crystals.) in limestone.

Amethyst-Hardness 7. A rare gemstone found near Copper Harbor, Keweenaw Peninsula. Purple variety of quartz.

Halite- Salt. Hardness 2. Cubic shaped crystals formed by evaporation. Large deposits of this mineral occur in Wayne County, southeastern Lower Michigan.

Pyrite- "Fools Gold". Hardness 6.0-6.5. Pale yellow in color and is confused with gold, so called, "Fools Gold". Found throughout Michigan and is the most common iron sulfide.

Jasper- Hardness 7. A variety of quartz occurring in many colors but usually red, from Marquette County in the Upper Peninsula.

Hematite- Hardness 5-6. Abundant iron ore mineral found throughout the Upper Peninsula. This variety is called Specular Hematite.






Favosite Coral

Favosite 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.






Lake Superior Beach Stone

These opaque stones were 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.






This  yellow green mineral is found throughout the world, but most notably in Austrialia, South Africa, Germany, and the United States, In the Keeweenaw 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, and Hemimorphite. Prehnite can be distinguished because it is harder than these three other minerals. Smithsonite has 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 aluminium. 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 is Dolomite, one of the oldest on the planet. Dolomite is an ancient rock in which formations of fossilized algae occur. These beautiful gemstones began as some of the first life on earth! Each specimen of this rock is a minimum of 2.2 billion years old! That's older than diamonds and half as old as the planet itself! This sublime specimen, Kona Dolomite, comes from Michigan's Upper Penninsula. It is named for the Kona HIlls south of Marquette where it is mined. These fossil formations are found in the lower eras of the Middle Precambrian Period. It is found in a variety of natural colors, brown, yellow, cream, red, and orange with shades of brown, cream, gray and blackmottling, banding and lacing.






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 Irelan

d; 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 various colorations within the gemstone, Commonly found colors are pink, tan, white, red and brown. Thomsonite with green, gray or blackgrounds or green eyes are the most highly prized and least found.

Thomsonite specimens are usually small. A little finger nail size stone with a good radiating pattern can be considered a nice specimen. Look for white, chalky, small round or almond shaped nodules in the rock.  Getting Thomsonite out of the rock is difficult without damaging them.

Thomsonite is also called:

Eyestone (eye agate)

Lintonite- 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 from the Lake Superior region of

Michigan and Minnesota.




Lake Superior Agate

Lake Superior agates are the oldest on Earth. 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. Said to enhance creativity, agates have special properties. They are found throughout the northern United States having been spread to the original Lake Superior region by glaciation.

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. 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.

A book written by Scott F. Wolter, "The Lake Superior Agate" and "The Lake Superior Agate- One Mans Journey" are great sources of information.









Last Updated on Tuesday, 12 May 2009 16:44




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Linda Michaels

313 E Lake Street
Petoskey, MI 49770