Jasper Knob is a bald-topped
hill within the city of Ishpeming composed entirely of jaspilite, or
more properly, banded hematite and jasper. Jasper is a kind of dense,
opaque quartz with crystals too small to be visible. Michigan jasper
is a deep red. This huge outcrop, locally touted as “the world's
largest gemstone,” forms a dramatic knob with a good view on the
southeast edge of Ishpeming. |
 Satellite photo of Jasper Knob (provided by DigitalGlobe & Google Earth) |
| Jasper Knob is a world-class
locality for observing BIFs (banded iron formations), an unusual "extinct"
sedimentary rock. The entire hill is composed of jaspilite, which consists
of alternating bands of red chert (jasper; cryptocrystalline quartz
- SiO2), red hematite (iron oxide - Fe2O3), and silvery-gray specular
hematite (iron oxide - Fe2O3). |
 This photo was snapped facing East (note person in the distance). It's truly an amazing experience being up there. I can only imagine what the American Indians must have thought of this natural wonder. |
 BIFs (banded iron formations of Jasper and Hematite) |
The jaspilite at Jasper
Knob is slightly metamorphosed and has nicely convoluted, warped, and
folded bedding. It makes up part of the Negaunee Iron-Formation (upper
Menominee Group, Marquette Range Super group), which is mid-Paleoproterozoic
in age (2.11 billion years; revised dates published in the 2000s indicate
this unit is 1.874 billion years old). Elsewhere in the Negaunee and
Ishpeming area, lithologies in this formation vary from jaspilites to
specularites to taconites, etc. |
 BIFs (banded iron formations of Jasper and Hematite) |
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 Jasper Knob also provides a nice view of Ishpeming. This pic was snapped facing North. |
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The stately wall around it makes it look like a public park. Actually
it's owned by Cleveland-Cliffs Iron Co., which does not encourage visitation
because of liability. The public is allowed on the property, though
footing is difficult here. Shown above is a basic map centered on down
town Ishpeming including several businesses and landmarks for reference. |
