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Named stone

Iron Hill jasper

Also called Iron Hill/Chestnut Hill jasper, Delaware Chalcedony Complex jasper (the wider group it belongs to)

A kind of jasper

Iron Hill jasperJasperMid-Atlantic

Description

Iron Hill jasper comes from Iron Hill and the neighbouring hills around Newark, Delaware, and across the line in Cecil County, Maryland. It is part of what archaeologists call the Delaware Chalcedony Complex, a cluster of jaspers, cherts and chalcedonies of mixed quality. The stone formed as the Silurian Iron Hill Gabbro weathered deeply, leaving iron oxides with ferruginous jasper, sometimes with thin seams of drusy quartz. It is usually yellow-brown but runs from yellow to dark brown and black, is rich in chlorite and often shows watery chalcedony banding. Quality ranges from excellent to poor. Several prehistoric quarries are recorded, including Iron Hill Cut, Iron Hill School and the Cooch Complex, and Paleoindian people favoured the high-grade jasper and chalcedony from these outcrops.

How to identify it

Colour
Typically yellow-brown, ranging from yellow to dark brown and black.
Inclusions
Rich in chlorite; often shows hydrous chalcedony banding (DelDOT); thin seams lined with drusy quartz (Delaware Geological Survey).

Geology

Ferruginous jasper left in the deep weathering zone of the Silurian Iron Hill Gabbro, with limonite, goethite and hematite. The same iron ores drew colonial miners to Iron Hill from the 1600s.

Where it comes from

Mid-Atlantic

States

Quarries and outcrops

  • Iron Hill, southwest of Newark, New Castle County, Delaware (Iron Hill School quarry 7NC-D-34; Cooch Complex 7NC-D-108)
  • Iron Hill Cut Jasper Quarry, Cecil County, Maryland (18CE65; NRHP 1983)
  • Heath Farm quarry, Cecil County, Maryland (18CE8)
  • Chestnut Hill and Gray's Hill (same gabbro hills)

Used by

  • Paleoindian: high-quality jasper and chalcedony from the Iron Hill outcrops were preferred for tools (DelDOT Series 98, citing Custer and Galasso 1980)
  • The Iron Hill Cut quarry's National Register record spans about 7000 B.C. to A.D. 1000

Look-alikes

Stones that are easy to confuse with Iron Hill jasper.

  • Pennsylvania (Hardyston, Reading Prong) jasper: chemically distinct (Blackman 1974, summarized by Stevenson and others)
  • Coastal Plain jasper pebbles on the Delmarva Peninsula, which come from stream gravels rather than the quarries

Sources

  1. Delaware Department of Transportation. Archaeology glossary: Jasper; Iron Hill Jasper.deldot.gov (opens in a new tab)
  2. Delaware Department of Transportation. Ronald McDonald House Site (7NC-B-54). DelDOT Archaeology Series 180, chapter 3.0 Natural Setting.deldot.gov (opens in a new tab)
  3. University of Delaware Center for Archaeological Research. 1992. Route 301 cultural resources planning study, Introduction. DelDOT Archaeology Series 98.deldot.gov (opens in a new tab)
  4. Delaware Geological Survey. Iron Hill Gabbro (unit description, from Schenck, Plank and Srogi 2000, GM10).dgs.udel.edu (opens in a new tab)
  5. 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)
  6. National Park Service. Iron Hill Cut Jasper Quarry Archeological Site, National Register of Historic Places record 83003754 (listed 1983).npgallery.nps.gov (opens in a new tab)
  7. 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)

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