Maquoketa Chert
See Also: Swan River Chert
Distribution: Parts of southeastern Minnesota. The extent of distribution is not known, but is probably limited.
Geologic Context: Apparently Upper Ordovician, Maquoketa Formation (although this has not been confirmed by observing the material in a bedrock context).
Main References: Gonsior 1992
Diagnostic Features: The medium to light grey color does not vary much. Resembles Swan River Chert in texture and overall appearance. Cobbles show a distinct concentric layered structure (like an onion), which may not be apparent in smaller pieces.
Metamorphosed Siltstone See siltstone
Moline Chert
Distribution: Western Illinois
Geologic Context: Pennsylvanian
Main References: Birmingham and Van Dyke 1981; Withrow and Morrow 1981
Diagnostic Features: Distinctive bluish grey color; minimal color variation. Fine grained speckling, consisting of bits of carbonized plant material.
Moss Agate See Gunflint Silica

Romano (1991) reports that Gunflint Silica has occasionally been misidentified as Moss Agate at archaeological sites in Minnesota. Moss Agate is actually a different material of more westerly origin.

Natural Brick See porcellanite
Nehawka Flint See Fusulinid Chert
Obsidian
Other Names: Natural glass
See Also: Fused glass
Distribution: The nearest source is probably in the Rocky Mountains in the western United States (e.g., the obsidian cliff in Yellowstone Park).
Main References: On identification of the sources of obsidian used in the Midwest, e.g. Anderson et al. 1986.
Oneota Chert See Prairie du Chien Chert

The Prairie du Chien Formation has two members, Oneota and Shakopee, both of which contain chert. In Minnesota, it is not generally possible to distinguish these two members (Austin 1972b:466) or the cherts they contain. In other areas, Oneota and Shakopee cherts might be considered to be separate materials.

Oolitic Jasper See Jasper Taconite
Pebble Chert See Red River Chert

It is presently unclear whether this name might also be used to refer to Hudson Bay Lowland Chert.

Petrified Wood See silicified wood
Porcellanite
Other Names: Metamorphosed siltstone, baked shale, Powder River Chert, fired brick, natural brick; also, more specifically, Fort Union Porcellanite.

According to Fredlund (1976:207), Powder River Chert is another name for porcellanite. However, it appears that this name is also used to refer to a distinctive chert found in the Badlands of western South Dakota.

Distribution: Western North Dakota, parts of Montana and Wyoming
Main References: Clayton et al. 1970:288-289; Fredlund 1976
Porous Quartzite See Swan River Chert
Powder River Chert See porcellanite

According to Fredlund (1976:207), Powder River Chert is another name for porcellanite. However, it appears that this name is also used to refer to a distinctive chert that is found in the Badlands of western South Dakota.

Prairie du Chien Chert
Other Names: Shakopee Chert and Oneota Chert are geologically distinct varieties of Prairie du Chien Chert. In Minnesota, however, the Shakopee and Oneota formations are not always distinguishable (Austin 1972b:466), and neither are the cherts they contain visually distinguishable. In other areas, Oneota and Shakopee cherts may be considered to be separate materials.
See Also: Red River Chert
Distribution: South central and southeastern Minnesota, northeastern Iowa, western and southern Wisconsin and possible parts of eastern Wisconsin
Geologic Context: Lower Ordovician, Shakopee and Oneota formations (formerly Prairie du Chien Formation; sometimes Prairie du Chien Group; Austin 1972b:466)
Main References: Gonsior 1992; Withrow 1983:40, 45-50
Diagnostic Features: PDC comes in three varieties. The first is easily distinguished by the presence of numerous ooliths. It is easily distinguished from Jasper Taconite, the only other oolitic raw material documented in the state, by its light color. PDC is very light to medium grey; when heat treated, it may have a reddish tinge but this never approaches the distinctive dark red color of Jasper Taconite. The texture of a fracture surface is normally somewhat rough.

The second variety of PDC is not as easily distinguished. It occasionally has a banding or grain, but this also occurs in Red River Chert. Because the distribution of these two materials does not overlap to a significant degree, they may still be distinguished based on the location of the site. The banding in this variety of PDC is contorted, somewhat like wood grain in a knot.

The third variety is sometimes described as "sandy." It is finer in grain, and displays fine mottling. The range of characteristics of this variety require additional study.

The color of all varieties is white to light or medium grey; it may be pale reddish or purple when heat treated. According to Webers (1972:477) and Stauffer (1937a, 1937b), PDC may also be fossiliferous.

Quarries: St. Croix River Access Site, 21 WA 49 (Hoffman and Myster 1992); LeSueur (Roetzel and Strachan 1992)
Pseudoquartzite See Tongue River Silica
Quartz
Distribution: Widespread in Minnesota, probably available in all glaciated parts of the state.
Diagnostic Features: Breaks along crystal surfaces; break shows many flat planes at various angles. Flake morphology not usually apparent. Translucent to transparent. Commonly colorless or white, although some pieces may be pale yellow, grey, or rarely bluish black.
Quartzite
See Also: Alma Quartzite, Hixton Quartzite, Sioux Quartzite
Distribution: Widely available in Minnesota, probably in all parts of the state where there is glacial drift.
Geologic Context: Precambrian, various formations; possibly other
Diagnostic Features: Individual sand grains visible. Translucent. Color for drift derived quartzites normally yellow to gold, or pink to purple, occasionally white. Drift derived quartzites usually brittle, marginally suitable at best for knapping. Hixton distinguished by whitish cementing material between the grains. This is lacking in drift derived quartzites.
Recrystallized Rhyolite See rhyolite

The relationship (and distinction) between the materials called rhyolite, recrystallized rhyolite and Lake of the Woods Rhyolite is not clear at this time.

Red River Chert
Other Names: Pebble Chert (It is presently unclear whether the name "Pebble Chert" might also be used to refer to Hudson Bay Lowland Chert.)
See Also: Cathead Chert, Selkirk Chert
Distribution: Northwestern, west central, central and southwestern Minnesota; eastern North Dakota; southeastern Manitoba; presumably eastern South Dakota and possibly northwestern and north central Iowa
Main References: Bakken 1985, 1993
Diagnostic Features: Usually very opaque. Molds of crinoid stem sections and other fossils are not uncommon. Never contains the white specks which characterize Galena Chert.
Rhyolite
Distribution: Northwestern Minnesota, and probably through much of central to southern Minnesota. Possibly also southeastern Manitoba.
Geologic Context: Precambrian, various formations
Main References: Bakken 1985, 1993
Diagnostic Features: Olive green to grey to colorless and translucent; streaks and patches of orange brown sometimes present. Scattered transparent phenocrysts in many samples. Always translucent to some degree. If light is not transmitted through even a thin edge, the material may be siltstone.
Quarries: See Lynch and Lovis 1988; McDougall 1980
Root River Chert See Cedar Valley Chert
Selkirk Chert See Red River Chert

The terms "Selkirk Chert" and "Red River Chert" are not precisely synonymous. The latter is a broader category, and includes the materials known as Cathead Chert. It Cathead or Selkirk cherts can be specifically identified, it is probably preferable to use these more specific names. This is the usual practice in Manitoba, where both materials occur in outcrops. In Minnesota, however, these materials are mixed in the drift. Because their characteristics (and distribution) overlap, the broader term "Red River Chert" was coined (Bakken 1985) to cover these materials when drift derivation made it hard to separate them.

Shakopee Chert See Prairie du Chien Chert

The Prairie du Chien Formation has two members, Oneota and Shakopee, both of which contain chert. In Minnesota, it is not generally possible to distinguish these two members (Austin 1972b:466) or the cherts they contain. In other areas, Oneota and Shakopee cherts might be considered to be separate materials.

Shell Rock Chert
Distribution: Limited area in south central Minnesota
Geologic Context: Upper Devonian, Shell Rock Formation
Main References: Bakken 1995b; Olmanson et al. 1994
Diagnostic Features: Colonial coral fossils visible in all parts of the chert. Chalky white cortex also displays coral structure. Color white to light grey. Somewhat translucent.
Quarries: Possibly Sherbuns Creek (Olmanson et al. 1994)
Silicified Shale See siltstone
Silicified Wood
Other Names: petrified wood, agatized wood, fossilized wood
Distribution: Occurs rarely in northwestern and west central Minnesota, more common in parts of southern Minnesota. Several varieties of silicified wood are found in parts of North Dakota and South Dakota. Small amounts of silicified wood have also been identified in the Pleistocene age Souris Gravels in southern Manitoba (Klassen 1969:2-9; cf. Syms 1977:32).
Diagnostic Features: Distinctive wood structure, apparent visually or in breakage patterns. Color generally stronger, less "smoky" or diffuse than KRF.
Siltstone
Other Names: argillite, argillite-quartzite, felsite, Knife Lake Siltstone, silicified shale, Lake of the Woods Chert

The specific term "Knife Lake Siltstone" implies origin from outcrops in the vicinity or Knife Lake, on the Minnesota-Ontario border. Primary deposits of siltstone are much more widely spread than this, however, and secondary deposits are even more widely spread. Therefore it is recommended that the less specific term "siltstone" be used instead in most cases, because it does not imply a specific geographic origin.

"Lake of the Woods Chert" generally refers to a finer textured, higher quality, black colored variety of siltstone. This is presumably more common in the vicinity of Lake of the Woods (Jon Nelson, personal communication 1992).

Distribution: Northeastern and east central Minnesota. Possibly northwestern and west central Minnesota.
Geologic Context: Precambrian, various formations
Main References: Fox 1980:129, 136, 140; Romano 1991
Diagnostic Features: A pale greenish grey patination, which seems to form relatively quickly. Slightly porous. Bedding planes may be seen in larger pieces. Some pieces contain a swirling grain of narrow, alternating light-and-dark bands, or sand like inclusions. Some pieces homogenous in color and texture. If a piece is not completely opaque, even on thin edges, it may be rhyolite instead.
Quarries: Bradbury Brook, 21ML42 (Malik and Bakken 1991, 1993)
Silver Hill Quartzite See Hixton Quartzite
Silver Mound Quartzite See Hixton Quartzite
Sioux Conglomerate Jasper
See Also: jasper, Jasper Taconite, Sioux Quartzite
Distribution: Outcrops very limited, restricted to the basal conglomerate of the Sioux Jasper in southwestern Minnesota. Glacial and fluvial redistribution of Sioux Conglomerate Jasper is not documented, but is probably minor.
Geologic Context: Late Precambrian
Main References: Austin 1972a:450-453; Morey 1972:3; Peterson et al. 1989:195
Sioux Quartzite
See Also: quartzite, Sioux Conglomerate Jasper
Distribution: "The Sioux Quartzite crops out in three areas in MinnesotaŅin northern Rock and southern Pipestone Counties, in the extreme southwestern part of the state; in northern Cottonwood; and in Nicollet County, along the Minnesota River east of New Ulm" (Austin 1972a:450). Glacial and fluvial redistribution of Sioux Quartzite is not documented.
Geologic Context: Late Precambrian
Main References: Austin 1972a:450-453; Morey 1972:3
Diagnostic Features: Pale, greyish pink color
Note: Sioux Quartzite was probably seldom used for flintknapping. Fractured pieces of this material do occur at archaeological sites in southwestern Minnesota, but they seldom have obvious flake characteristics. The significance of their presence at sites in not clear.
Swan River Chert
Other Names: porous quartzite, drusy quartzite
Distribution: Northwestern, west central and southwestern Minnesota; southeastern Saskatchewan; southern Manitoba; eastern North Dakota; presumably eastern South Dakota and possibly north central and northwestern Iowa portions of west-central and southern Manitoba, southern Saskatchewan, southeastern Alberta, northern Montana (Low 1996:165)
Geologic Context: Possibly Paleozoic
Main References: Bakken 1985, 1993; Campling 1980; Leonoff 1970 (cited in Syms 1977); Low 1996
Diagnostic Features: SRC lacks the uniformity of an actual quartzite. The fracture surface has a pebbly, "orange peel" texture. Usually the cortex of an SRC cobble has a distinctive pitted, ropy or spongelike appearance which is difficult to describe but easily recognized after it has been observed on a few specimens. SRC commonly has irregularly shaped vugs, which are sometimes lined with quartz druse. It is almost always seen, especially when viewed against a light, to contain small, nebulous "clouds" or feathery banding. When viewed under a low power microscope, the structures are often seen to have concentric banding, much like microscopic agates. Rare pieces lack this visual patterning, and have a somewhat coarse "chalcedonous" appearance. The color of SRC varies widely, and should not be used as a diagnostic characteristic.
Quarries: Greenbush Borrow Pit, 21RO11 (Peterson 1973)
Taconite See Jasper Taconite
Taconite Jasper See Jasper Taconite
Tongue River Silica
Other Names: arenaceous chert, pseudoquartzite, Tongue River Silicified Sediment

"Tongue River Silicified Sediment" is an earlier name for this material. Anderson (1978) suggested that "Tongue River Silica" was a preferable name, a usage which has since become well (although not universally) established.

There are different varieties of TRS, distinguished on the basis of color and texture: yellow/red versus grey; and fine grain versus coarse grain. It seems that color provides the most consistent and widely used way to distinguish varieties. Distribution of the grey varieties of TRS appears to be confined to the Dakotas. The information presented here relates primarily to yellow/red TRS, which has a more widespread distribution and occurs naturally in Minnesota.

Distribution: North Dakota; central and parts of southern Minnesota; central and eastern South Dakota; northwestern Iowa
Main References: Ahler 1977; Anderson 1978; Bakken 1985, 1993; Porter 1962
Diagnostic Features: The presence of root molds, usually unfilled but sometimes as filled casts. A unique, sugary sparkle on fracture surfaces. Very opaque. The natural golden brown color is distinctive, and does not vary a great deal. The deep red color produced by heat treating is also distinctive, although it appears that moderate ("incomplete") heat treatment may result in a more neutral grey color. Usually opaque. Rarely confused with other raw materials in the region.
Tongue River Silicified Sediment See Tongue River Silica
Waxy Brown Chert See Rainy Butte Silicified Wood
West Patricia Chert See Green Recrystallized Chert


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