Jasper taconite

Also called JT, Gunflint jasper, Animikie silicate (in part)

A kind of jasper

Jasper taconiteJasperMidwest/Ohio Valley

Description

Jasper taconite is a deep blood-red jasper from the Gunflint Iron-Formation, a Middle Precambrian rock roughly 1.7 to 2 billion years old that runs from northeastern Minnesota into northwestern Ontario. It is packed with small round granules of iron oxide that look like tiny eggs, and they make up much of the stone. It is opaque, with a pebbly break and a waxy to dull lustre. Bedrock quarries are known near Thunder Bay, Ontario, and good cobbles occur in the drift of northeastern Minnesota; farther west the nodules are small and crumbly. It was used most in the Paleoindian period, especially at late Paleoindian quarry camps on old Lake Superior beaches, but people kept using it throughout prehistory. Heat does not improve it.

How to identify it

Colour: Normally deep red; dark green, dark blue or nearly black pieces occur but are rare (Bakken). Black to bluish grey where magnetite outweighs hematite (Lindenberg).
Texture: Opaque with a pebbly fracture surface caused by the dense iron-oxide granules in a fine chalcedony matrix (Lindenberg). Flakes better than Knife Lake siltstone, but low-grade pieces break along blocky joints (Romano, via Lindenberg).
Luster: Waxy and glossy to rather dull on fresh breaks (Lindenberg).
Inclusions: Small round granules that look like ooliths dominate the stone; the clear matrix fills only the gaps between them (Bakken). Granules can make up about 40 percent and many are solid hematite or magnetite (Lindenberg).
Cortex: Weathered pieces stay much the same; heavy weathering gives a slightly rusty look (Lindenberg).
Heat treatment: Not improved by heating. After 6 hours at 500-600 degrees the matrix turned opaque granular bluish grey and fell apart when knapped (Romano, via Lindenberg).

Geology

Part of the Gunflint Iron-Formation of the Middle Precambrian Animikie Group, about 120 m thick and dated between about 1.7 and 2.0 billion years. Iron minerals settled in shallow seas and silica then cemented the sediment. Jasper taconite, Gunflint silica and Kakabeka chert all come from this formation and can grade into each other (Lindenberg). Bakken suggests "Animikie silicate" as a blanket name when a piece cannot be pinned down.

Where it comes from

Midwest/Ohio Valley

States

Minnesota

Quarries and outcrops

Gunflint Iron-Formation outcrops, northeastern Minnesota and northwestern Ontario (Lindenberg)
Cummins quarry site near Thunder Bay, Ontario (late Paleoindian; miles of exposed jasper per Steinbring, via Bakken)
Stream cuts and beaches of glacial Lake Minong (Lindenberg)
Glacial drift of the Eastern Resource Region, northeastern Minnesota; poor small nodules farther west (Bakken)

Used by

Late Paleoindian: dominant stone at the Cummins quarry-workshop (dated about 8,500 BP) and nearly the only stone at the Brohm site, 8,000-9,000 BP (Lindenberg; Mulholland et al. 2011)
Quetico-Superior and Lakehead complex assemblages are rich in it (Lindenberg)
Lake Superior North Shore sites in Minnesota: the most common stone at several Region 9 sites (Mulholland et al. 2011)
Carried along the Lake Superior to Lake Winnipeg waterway; one report places it as far east as Pennsylvania (Lindenberg)

Look-alikes

Stones that are easy to confuse with Jasper taconite.

Gunflint silica and Kakabeka chert from the same formation; pieces can grade between them (Bakken; Lindenberg)
A jasper facies of the Biwabik Iron-Formation (Mesabi Range), with no known prehistoric surface exposures (Lindenberg)
Other "jasper" from Minnesota iron-mine areas, such as ochre-coloured flakeable stone in mine tailings at Virginia, Minnesota (Bakken)

Sources

Lindenberg, Sheila Marie. 1996. Source Characterization of Western Lake Superior Region Lithics Using Neutron Activation Analysis: A Geoarchaeological Study. M.S. thesis, University of Minnesota.conservancy.umn.edu (opens in a new tab)
Bakken, Kent E. (written about 1995; PDF issued later). Chipped Stone Raw Materials. Chapter 6 in Stone Tools of Minnesota. Minnesota Office of the State Archaeologist, St. Paul.mn.gov (opens in a new tab)
Mulholland, Susan C., Stephen L. Mulholland, Jennifer R. Hamilton, and Stacey Stark. 2011. Points and Pits: Archaeological Investigations in Minnesota's Region 9, the Lake Superior Shore, Carlton, Cook, Lake, and St. Louis Counties, Minnesota. Duluth Archaeology Center Report 11-22.mn.gov (opens in a new tab)

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