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Named stone

Oriskany stones: Ridgeley quartzite and Shriver chert

Also called Ridgely quartzite, Ridgely Sandstone Member, Shriver chert, Shriver Member chert

A kind of quartzite

Oriskany stones: Ridgeley quartzite and Shriver chertQuartziteMid-Atlantic

Description

The Oriskany Formation of western Maryland gave knappers two quite different stones. Ridgely (also spelled Ridgeley) quartzite is a white, tan, gray or pink sandstone cemented so tightly with silica that it has a fine, sugary texture with few flaws or bedding planes. Shriver chert is dark blue-black, found as nodules and as thin beds separated by dark shale bands, and it wears a paler weathered patina. The many bedding planes in the bedded form make it harder to work, and it may hold fossils and calcareous patches. Shriver chert also marks the contact between the Oriskany and the older Helderberg rocks. State guides sample both near Flintstone and Spring Gap in Allegany County, Maryland.

How to identify it

Colour
Ridgely quartzite: white, tan, gray and pink. Shriver chert: dark blue-black in both nodular and bedded forms.
Texture
Ridgely: homogeneous, fine grained and sugary with few flaws or visible bedding. Shriver: bedded forms have many bedding planes that can reduce workability.
Inclusions
Shriver chert may contain fossils and calcareous parts, and thin dark shale bands separate its beds.
Cortex
Shriver chert has a lighter weathered patina.

Geology

Both stones come from the Oriskany Formation. Ridgely quartzite is the Ridgely Sandstone Member, a sedimentary orthoquartzite hardened by silica cement. Shriver chert comes from the lower Shriver Member and is the stratigraphic marker for the Oriskany/Helderberg contact; cherty siltstone from the same member was also used. The Maryland guide cites Shriver chert as its example of a bedded chert.

Where it comes from

Mid-Atlantic

States

Quarries and outcrops

  • Flintstone, Allegany County, Maryland (Ridgely quartzite sample)
  • Near Spring Gap, Allegany County, Maryland (Shriver chert sample)
  • Ridgeley, Mineral County, West Virginia (type locality of the Ridgeley Sandstone)

Used by

  • Used prehistorically, but the Virginia pages name no culture, period or point type

Look-alikes

Stones that are easy to confuse with Oriskany stones: Ridgeley quartzite and Shriver chert.

  • Helderberg chert from the beds just below the Oriskany contact
  • Other sugary orthoquartzites such as Erwin/Antietam quartzite of the Blue Ridge

Sources

  1. Ebright, Carol. 1999 (updated 2023). Ridgely Quartzite. Virginia Department of Historic Resources, Lithics (Projectile Points and Lithics guide).dhr.virginia.gov (opens in a new tab)
  2. Ebright, Carol. 1999 (updated 2023). Shriver Chert. Virginia Department of Historic Resources, Lithics (Projectile Points and Lithics guide).dhr.virginia.gov (opens in a new tab)
  3. Maryland Archaeological Conservation Laboratory. Chert. Diagnostic Artifacts in Maryland: Common Stone Types (Jefferson Patterson Park and Museum).apps.jefpat.maryland.gov (opens in a new tab)
  4. U.S. Geological Survey, National Geologic Map Database. Geolex: Ridgeley; and Geolex: Oriskany.ngmdb.usgs.gov (opens in a new tab)
  5. U.S. Geological Survey, National Geologic Map Database. Geolex: Ridgeley.ngmdb.usgs.gov (opens in a new tab)

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