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Named stone

Brook Run jasper

Also called Brook Run quarry jasper

A kind of jasper

Brook Run jasperJasperMid-Atlantic

Description

Brook Run jasper comes from a single quarry, site 44CU122, in western Culpeper County, Virginia, on the eastern edge of the Triassic Culpeper Basin. The jasper sits in a narrow fault zone where siltstone and sandstone meet, as angular blocks of brecciated red to yellow jasper glued together by black chert, often with white rinds. It formed from hot fluids, with microbes helping lay down the silica, and fossil microbial filaments can be seen in thin section. People dug a pit several metres deep to reach it, but only for a short window: quarrying and bifacial blank making date to the very end of the Paleoindian period and the Early Archaic, roughly 10,000 years ago, and stopped soon after. No heat treatment is seen at the quarry. Its chemistry separates it from other Virginia jaspers.

How to identify it

Colour
Red to yellow jasper in brecciated masses, cemented by black chert; pieces often have white rinds.
Texture
Microcrystalline quartz; fractures filled with black chert.
Inclusions
Fossilized microbial filaments (seen petrographically).
Cortex
White rinds on angular jasper pieces.
Heat treatment
No evidence of heat treatment at the quarry (Virginia DHR).

Geology

Hydrothermal jasper formed with the help of microbes, found only within a narrow Triassic fault zone in the Culpeper Basin, where the quarry wall is red sandstone and siltstone. The basin holds intrusive volcanic and metamorphic rocks and several north-south faults.

Where it comes from

Mid-Atlantic

States

Quarries and outcrops

  • Brook Run quarry, site 44CU122, east of Brook Run, western Culpeper County, Virginia (Rapidan River drainage, Culpeper Basin)

Used by

  • Late Paleoindian and Early Archaic only, about 10,000 years ago (Virginia DHR); Early Archaic, 10,000-8,500 BP (Stevenson and others)

Look-alikes

Stones that are easy to confuse with Brook Run jasper.

  • Flint Run jasper and other Virginia jaspers (Bonifant, Arnolds Valley/Rockbridge, Virginia Beach pebbles); trace-element analysis (INAA) can separate the sources, eye alone cannot

Sources

  1. Egloff. 2008 (updated 2023). Brook Run Jasper. Virginia Department of Historic Resources, Projectile Points and Lithics guide.dhr.virginia.gov (opens in a new tab)
  2. Stevenson, Christopher M., Michael D. Glascock, Robert J. Speakman and Michelle McCartney. n.d. (about 2006). Expanding the Geochemical Database for Virginia Jasper Sources. Virginia Department of Historic Resources.dhr.virginia.gov (opens in a new tab)
  3. Monaghan, G. W., D. R. Hayes, S. I. Dworkin and E. Voigt. 2004. Geoarchaeology of the Brook Run Site (44CU122): An Early Archaic Jasper Quarry in Virginia, USA. Journal of Archaeological Science 31:1083-1092.sciencedirect.com (opens in a new tab)

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