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).