Delmarva and Chesapeake coastal chert and pebble jasper

Also called Coastal chert, Pebble jasper, Pebble chert, Aquia orthoquartzite, Coastal Plain gravel jasper and chert

Delmarva and Chesapeake coastal chert and pebble jasperChert (and flint)Mid-Atlantic

Description

On the Delmarva Peninsula and around the Chesapeake Bay, good bedrock stone is scarce, so people used what rivers and shores delivered. Coastal chert is white to cream or light tan, angular, and chalky when weathered. Its source is still a puzzle, and the points made from it on Delmarva are all Paleoindian. Pebble jasper and chert are the everyday stones: cobbles in coastal gravels, bigger upstream and smaller near the ocean, many probably washed down from Pennsylvania by the Susquehanna. Aquia orthoquartzite, a silica-cemented sandstone, was favoured for Paleoindian and Early Archaic points. Burial in tidal marsh can change surface colours, so jasper may look like plain chert.

How to identify it

Colour: Coastal chert: pure white to cream or light tan, orange-yellow where iron-rich, gray to black after burial in manganese-rich wet ground. Aquia orthoquartzite: white to brown, gray, tan, yellow or red when weathered, black to dark blue-gray when fresh in the Stafford area.
Texture: Coastal chert is angular, not water-worn. Aquia comes in a coarse form (larger quartz grains in an opal-like matrix) and a fine form (smaller sand grains in a chert-like matrix).
Inclusions: Aquia orthoquartzite can contain green glauconite that oxidises to tan, yellow or orange; iron staining gives reddish-brown (Egloff).
Cortex: Weathered coastal chert develops a chalky exterior.

Geology

Coastal chert occurs in secondary deposits along the Atlantic shore, especially on Virginia's barrier islands, and its original source 'remains an enigma'. The angular pieces were not carried far by water and are not tied to the Chesapeake paleochannels. Pebble jasper and chert are cobbles in ancient river gravels on the Coastal Plain: Upper Chesapeake Bay cobbles probably came from Pennsylvania via the Susquehanna, while Pocomoke River and Beasley Bay pieces may come from Potomac, Rappahannock and York River systems. Aquia orthoquartzite derives from the Aquia Formation, 150 to 250 feet below the present land and bay surface near Eastern Bay, with outcrops in Stafford County, Virginia, and Charles County, Maryland.

Where it comes from

Mid-Atlantic

States

Quarries and outcrops

Skidmore Island, Northampton County, Virginia (coastal chert sample)
Virginia Beach and the Eastern Shore of Virginia (pebble jasper and chert)
Martin Point, Talbot County, and the Pocomoke River, Somerset County, Maryland
Aquia Formation outcrops in Stafford County, Virginia, and Charles County, Maryland

Used by

Paleoindian: diagnostic points and scrapers of coastal chert on Delmarva are exclusively Paleoindian (Egloff)
Paleoindian and Early Archaic: the coarse Aquia orthoquartzite for points; Middle Archaic through Woodland: the fine-grained variety (Egloff)
Archaic: pebble materials were easier to reach at lower sea levels

Look-alikes

Stones that are easy to confuse with Delmarva and Chesapeake coastal chert and pebble jasper.

Jasper buried in tidal marshes can look the same as plain chert (Lowery and Wagner 2012, cited by the Maryland guide)
Quartzite and fine jasper cobbles occur together in the Delmarva gravels

Sources

Egloff. 2008 (after Lowery 2002). Coastal Chert. Virginia Department of Historic Resources, Lithics (Projectile Points and Lithics guide).dhr.virginia.gov (opens in a new tab)
Egloff. 2008 (after Geier 1990 and Lowery 2002). Pebble Jasper and Chert. Virginia Department of Historic Resources, Lithics (Projectile Points and Lithics guide).dhr.virginia.gov (opens in a new tab)
Egloff. 2008 (after Lowery 2002). Aquia Orthoquartzite. Virginia Department of Historic Resources, Lithics (Projectile Points and Lithics guide).dhr.virginia.gov (opens in a new tab)
Maryland Archaeological Conservation Laboratory. Jasper. Diagnostic Artifacts in Maryland: Common Stone Types (Jefferson Patterson Park and Museum).apps.jefpat.maryland.gov (opens in a new tab)

All materials