Connection to the Earth Science Curriculum
At Mohawk Mine visitors will observe waste rock/ poor rock left over from copper mining. Mohawkite might be found in this location.
Earth Science Literacy Principles-
Ÿ Big idea 2 Earth is 4.6 billion years old.
The formation of copper and mohawkite took a long time in geologic history.
Ÿ Big idea 4 Earth is continuously changing.
The formation of copper and mohawkite happened because of the changes that occurred to the Earth in geologic time.
ŸBig idea 7 Humans depend on Earth for resources.
Humans mined copper because of need for materials made out of copper.
The mountains and valleys we see today have always been on Earth.
The Earth has always been pretty much the way it is now.
The mountains and valleys took a long time to form and will change. Mining has also changed them
Ÿ Geological processes occurring over millions of years formed the continents, oceans, mountains, coastlines, and other landscapes, now those processes have stopped.
All rocks are more or less the same.
Rocks and minerals have different chemical compositions and properties. Rocks and minerals were formed from processes such as melting, cooling, heat, pressure, weathering, erosion, compaction and cementation.
Michigan State Science Content Expectations Addressed:
E.ES.M5 The lithospheric plates of the Earth constantly move, resulting in major geological events such as earthquakes, volcanic eruptions and mountain building.
E.SE.M4 Rocks and rock formations bear evidence of the minerals, materials, temperature/pressure conditions and forces that created them.
S.IP. 06. 13 Use tools and equipment appropriate to scientific investigations.
Key Earth Science/ Geological Vocabulary terms:
Basalt- dark-colored dense igneous rocks that form from magma rich in iron and magnesium.
Conglomerate- a sedimentary rock consisting of pebbles cemented together by finer particles.
Crystal- the external planar form or shape mineral assumes due to its internal ordered arrangement of atoms.
Deposition- the final step in an erosional process, in which sediments are dropped by running water, wind, gravity, or glaciers as their energy of motion decreases.
Erosion- the process that wears away surface materials and moves them from one location to another, usually by gravity, glaciers, wind or water.
Faults- surfaces along which rocks break and move; rocks on either side of a fault move in different directions relative to the fault surface.
Fracture- the physical property of a mineral that causes it to break with rough or jagged edges.
Glacier- a mass of snow and ice that moves slowly downhill due to its weight.
Rift- an area in the Earth’s crust that is spreading apart. The opening usually allows magma to come to the surface.
Lava- Magma that reaches the Earth’s surface.
Luster- the physical property of a mineral that describes how light is reflected from its surface.
Streak- the color of a mineral when it is powdered; usually observed by rubbing the mineral on a ceramic streak plate.
Weathering- the breaking of rocks into smaller pieces, either mechanically or chemically.
The area is managed by the Township of Allouez.
Date Visited: July 14, 2011
Mohawk Mine and Mohawkite EarthCache
In Allouez Township, Michigan, near Mohawk Mine, there are piles of waste rock where Mohawkite might be found.
Materials Needed for Visit
Information provided, GPS, a compass, a local rock/ mineral guide for Michigan, magnifying lens, hardness kit with a streak plate.
From Ahmeek, Michigan, travel north on US Route 41. Enter the town of Mohawk. Turn right on 6th Street. Travel until you see Bethany Lutheran Church on the right. The mine will be on the left. Use the GPS to find Mohawk Mine #4 remains.
Figure 1: Mohawk Mine Dump & Mill
History of the Keweenaw Peninsula
About a billion years ago, molten rock reached the surface in this area when the Midcontinental Rift formed. As these lava flows cooled they formed layers of basalt rock.
Figure 2 Source: Robinson, S. (2001) Is this an agate?: An Illustrated Guide to Lake Superior’s Beach Stones Michigan
Rift valleys formed here. Gas bubbles were trapped near the tops of cooling lava flows creating empty spaces in the basalt. During quieter periods of eruptions weathering and erosion of surrounding rocks covered the basalts and formed conglomerates. Over time layers of rock formed as more volcano flows occurred followed by more weathering and erosion cycling many times.
Figure 3 Source: Robinson, S. (2001) Is this an agate?: An Illustrated Guide to Lake Superior’s Beach Stones Michigan
Later, a continental collision caused the igneous and sedimentary rocks to become tilted, fractured, and faulted. Hot water moved inside the open spaces in the rocks. The hot water had dissolved copper and other minerals in it. In the next several hundred million years, seas covered the area and deposited sediments.
Figure 4 Source: Robinson, S. (2001) Is this an agate?: An Illustrated Guide to Lake Superior’s Beach Stones Michigan
There was more weathering and erosion. About 3 million years ago glaciers moved over the area and exposed the basalts that contained cooper, agate and other minerals. The glaciers retreated about 10,000 years ago.
History of Mohawk Mine
During the 1840’s to 1860’s copper ore was mined in this area. It contained more waste rock than copper. The copper had to be extracted from the rock. People separated the rocks before sending them to the stamp mills. After being stamped to the size of peas, a series of washing and separating machines requiring a lot of water were used to capture the copper mineral. The waste product from the mines were called poor rock because they did not have much value. The poor rock was piled up along side of shafts. This “rock pile” found at this site is that poor rock
Logging Question 1: Describe the rocks in the poor rock pile. Include the color and range of the rock sizes.
Figure 5: Mohawkite Sample Collected from Mohawk Mine
Mohawkite (Cu3As) is technically not a mineral but has a mixture of minerals in its composition. It is named for the place it can be found, Mohawk mine.
Mohawkite has some unique properties that can help with identification.
Appearance: It has a speckled white appearance on fresh surfaces. When exposed to air, it quickly tarnishes to brown.
Specific gravity is between 7.2 and 7.9.
Hardness: between 3 and 3.5.
Breakability: uneven fracture
Logging Question 2: Using the information about mohawkite’s properties, try to find a piece of mohawkite in the waste rock pile. How will you know it IS mohawkite?
Logging Question 3: Find a rock that is NOT mohawkite. What are some of its properties? How do you know it is not mohawkite?
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