JASPER KNOB
Jasper Knob (Jasper Hill) 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).
Jasper Knob is an ENE-WSW
elongated hill located in the southeastern part of the town of Ishpeming
(central Marquette County, northern Upper Peninsula of Michigan). It can
be accessed using steps at a small opening along a stone wall near the
intersection of Hill Street and Jasper Street. Jasper Knob is part of the
Marquette Iron Range.
GPS of hilltop: 46° 29.208'
North, 87° 39.275' West.
Satellite photo of Jasper
Knob
(provided by DigitalGlobe
& Google Earth)
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 Supergroup), 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.
Much of the north-facing
side of Jasper Knob is unfortunately obscured by paint and graffiti, but the
locality is still overwhelmingly impressive.
The Negaunee Iron-Formation
has been intensely mined in the UP for a long time as a source of iron for the
steel industry. Jasper Knob is still untouched by iron companies because
it reportedly has a relatively low iron content (supposedly about 40%).
Above: weathered jaspilite
exposure - the banded red & silvery-gray coloration is absent; Negaunee
Iron-Formation, mid-Paleoproterozoic, 2.11 billion years.
Beautiful sample of
jaspilite (banded iron formation/BIF) from the Negaunee Iron-Formation (2.11
b.y.). This rock is part of the Jackson Mine Monument, erected in a small
park on the north side of Rt. 41/Rt. 28 in the town of Negaunee (central Marquette
County, northern Upper Peninsula of Michigan).
