On the Wisconsin side!
Identifying Lake Michigan Rocks
& other treasures!
My personal Study Guide
Roughly the same area of beach on different days; the visible rocks change constantly.
The large rock (on the right) is on the beach I visit regularly; this one hasn't
really budged much in all the time I've seen it. Not surprised, it's huge!
The other two are also regular finds, but they do come and go day to day.
Basalt is composed mostly of oxides of silicon, iron, magnesium, potassium, aluminum, titanium, and calcium. Geologists classify igneous rock by its mineral content whenever possible; the relative volume percentages of quartz (crystalline silica (SiO2)), alkali feldspar, plagioclase, and feldspathoid (QAPF) are particularly important. An aphanitic (fine-grained) [b1] igneous rock is classified as basalt when its QAPF fraction is composed of less than 10% feldspathoid and less than 20% quartz, and plagioclase [b2] makes up at least 65% of its feldspar content. This places basalt in the basalt/andesite field of the QAPF diagram. Basalt is further distinguished from andesite by its silica content of under 52%.
Basalt is usually dark grey to black in colour, due to a high content of augite or other dark-coloured pyroxene minerals, but can exhibit a wide range of shading. Some basalts are quite light-coloured due to a high content of plagioclase; these are sometimes described as leucobasalts. It can be difficult to distinguish between lighter-colored basalt and andesite, so field researchers commonly use a rule of thumb for this purpose, classifying it as basalt if it has a color index of 35 or greater. (Wiki)
[b2] - Plagioclase...
is the most common and abundant mineral group in the Earth's crust. Part of the feldspar family of minerals, it is abundant in igneous and
metamorphic rock, and it is also common as a detrital[b3] mineral in sedimentary rock.It is not a single mineral, but is a solid solution of two end
members, albite or sodium feldspar (NaAlSi3O8) and anorthite or calcium feldspar (CaAl2Si2O8). These can be present in plagioclase in any proportion
from pure anorthite to pure albite. The composition of plagioclase can thus be written as Na1−xCaxAl1+xSi3−xO8 where x ranges from 0 for pure
albite to 1 for pure anorthite. This solid solution series is known as the plagioclase series. The composition of a particular sample of
plagioclase is customarily expressed as the mol% of anorthite in the sample. For example, plagioclase that is 40 mol% anorthite would be described
as An40 plagioclase
[b3] - Detritus is particles of rock derived from pre-existing rock through weathering and erosion
Brachiopods are the most abundant fossils in Wisconsin.
These crinoid fossils died 430 million years ago at the bottom of a shallow sea in the area now known as Wisconsin.
Tiny crinoid stems ('columnals') and discs (the individual discs along the columns) - so amazingly elegant
What do crinoids look like?
Granite is one of my favorite rocks; many collectors poo-poo granite because it is so abundant.
Phaneritic = is a term used to describe the texture of igneous rocks. It refers to rocks where the
individual mineral grains are large enough to be seen with the naked eye, indicating a slow cooling rate of the magma or lava.
Plagioclase = is the most common and abundant mineral group in the Earth's crust. Part of the feldspar family of minerals,
it is abundant in igneous and metamorphic rock, and it is also common as a detrital mineral in sedimentary rock. It is not a single mineral,
but is a solid solution of two end members, albite or sodium feldspar (NaAlSi3O8) and anorthite or calcium feldspar (CaAl2Si2O8).
Granite is typical of a larger family of granitic rocks, or granitoids, that are composed mostly of coarse-grained quartz and feldspars in varying
proportions. These rocks are classified by the relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification), with
true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals,
though a few (known as leucogranites) contain almost no dark minerals. Granite is nearly always massive (lacking any internal structures),
hard (falling between 6 and 7 on the Mohs hardness scale), and tough. These properties have made granite a widespread construction stone throughout human history.
Beach glass started out as bottles, jars, glasses, plates, windows, windshields, or ceramics; eventually these items were discarded and, in this case, dumped
into Lake Michigan. Over decades in the lake, they become smoothed and weathered by the action of the waves and sand. Thus creating beautiful beach glass. Below are
a few of my favorite pieces I have found in Milwaukee County, on the shining shores of Lake Michigan.
Ceramics are also discarded in the Lake. If one is lucky, you may find pieces with designs or colors that have not yet been worn away by the waves and sand!
[Images Coming soon]
Many of these are tiny; some have a bit of design or glaze still on the piece
What is Terrazzo?
Terrazzo is a composite material made of small chips of marble, granite, quartz, glass, or other materials embedded in a cementitious or epoxy matrix,
which is then polished to create a smooth and decorative surface.
These pieces were dumped into Lake Michigan in years past and found by me.
Concrete was dumped into Lake Michigan, after years of weathering and polishing, the beach has provided us with wonderful treasures.
Man-made iron slag dumped into Lake Michigan...during the heyday of iron production
Likely from The Neda Iron Mine, an Ordovician sedimentary iron deposit, mined/smelted in the Milwaukee area from 1845 to 1928.
The ore was processed locally in Mayville, Wisconsin and at smelters in Milwaukee and Chicago.
Milwaukee has a significant history of heavy industry, including tanneries, breweries, and metalworking plants situated along its rivers.
Past industrial practices often involved dumping waste directly into the rivers and the lake, including materials containing heavy metals like iron, before modern pollution control
regulations were in place.
VIDEOS
At this time in Earth's history, Wisconsin was SOUTH of the equator!
Chain Coral Fossils
Favosite Coral Fossils
Granite
However, there is such a wide variety of colors,
granite really makes the beach pop!
Granite (/ˈɡrænɪt/ GRAN-it) is a coarse-grained (phaneritic) intrusive
igneous rock composed mostly of quartz, alkali feldspar, and
plagioclase. It forms from magma with a high content of silica and
alkali metal oxides that slowly cools and solidifies underground. It is
common in the continental crust of Earth, where it is found in igneous
intrusions. These range in size from dikes only a few centimeters across
to batholiths exposed over hundreds of square kilometers.
Rugose 'Horn' Coral Fossils
Among the natural objects one finds on the beach (see above) there are also remnants of man-made items that have been discarded and dumped into the lake. Most people think of these things as just 'junk',
however, I think they are elegant reminders of what the surf and sand can do to lead, glass, pottery, and building constructs after decades in the water.
Beach Glass
Pottery Shards 
Terrazzo
Although they are manmade, after the beach weathers them, they are really
quite elegant! 
Concrete 
Iron Slag 
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