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Silicified wood and other silicified sediments, photo 1
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Rock type

Silicified wood and other silicified sediments

Also called Petrified wood, Silicified wood, Silcrete, Porcellanite, Clinker, Silicified sandstone, Silicified mudstone

Silicified wood and other silicified sedimentssilica-replaced wood and silica-cemented or baked sedimentAll regions

2 photos

Description

Petrified (silicified) wood is wood whose cells were replaced by silica; when fully silicified it can flake well, though quality varies widely. In Virginia fresh breaks are dark yellow-brown to gray, weathering to banded blue, purple and white, and Clovis points exist in it. North Dakota's Rainy Butte chert is iron-rich fossil wood in chocolate brown, used for Clovis tools. The page also covers other silica-hardened sediments: silcrete (silica-cemented soil, as in the Taylor and Rhame beds), silicified sandstone and mudstone in Maryland and Virginia, and clinker or porcellanite, the red rock baked above burned coal seams. Texas coastal gravels also hold silicified wood, and a San Patrice point from McFaddin Beach is made of it.

How to identify it

Colour
Fresh breaks dark yellow-brown, translucent or gray, weathering to banded deep blue, purple and white (Virginia); chocolate brown in Rainy Butte chert; silcrete gray to cream, sometimes iron-stained; clinker reddish.
Texture
Excellent flaking when highly silicified; silcrete is very hard; clinker is brick-like.
Luster
Waxy where wind-polished (silcrete).
Inclusions
Growth rings and cell structure in wood; molds of horsetail and branches in silcrete; fossils in silicified sandstone and mudstone.

Geology

Petrified wood in Virginia comes from Triassic gravel deposits east of the Fall Line along the James, Appomattox, Nottoway and Meherrin rivers, where eroding banks expose log-like pieces. In North Dakota, Rainy Butte chert occurs in the upper Sentinel Butte Formation and is iron-rich fossil wood. The Taylor Bed is a silcrete capping the Bear Den Member of the Golden Valley Formation, thought to have formed from silica-rich ooze at the base of a swamp, and the Rhame Bed silcrete marks the Slope Formation contact. Clinker forms where lignite seams burn and bake the nearby clay, shale and sandstone to natural brick. Mississippi has chalcedony-replaced fossil palm wood.

Where it comes from

All regions

States

Quarries and outcrops

  • Fall Line and interior Coastal Plain, Richmond south to North Carolina (Point-of-Rock site, Chesterfield County, Virginia)
  • Rainy Buttes, Billings County, North Dakota
  • Taylor Bed and Rhame Bed, southwestern North Dakota
  • Choptank and Wye rivers, Maryland (silicified sandstone) and Accomack and Northampton counties, Virginia (silicified mudstone)
  • McFaddin Beach, Jefferson County, Texas (San Patrice point)
  • Western North Dakota badlands (clinker, locally called scoria)

Used by

  • Clovis and Early Archaic points and end scrapers of Virginia petrified wood (Egloff)
  • Clovis biface of Rainy Butte chert and a silcrete projectile point from western North Dakota (Murphy)
  • Paleoindian San Patrice point of silicified wood on the Texas coast (Texas Beyond History)

Look-alikes

Stones that are easy to confuse with Silicified wood and other silicified sediments.

  • Chert and flint (without wood structure)
  • Agatized coral (silicified coral)

Sources

  1. Egloff (after McAvoy 1979). 2008. Petrified (Silicified) Wood. Virginia Department of Historic Resources, Lithics (Projectile Points and Lithics guide).dhr.virginia.gov (opens in a new tab)
  2. Murphy, Ed. 2014. Knife River Flint and Other Siliceous Rocks in Western North Dakota. Geo News (January 2014), North Dakota Geological Survey.dmr.nd.gov (opens in a new tab)
  3. Bluemle, John P. North Dakota's Clinker. North Dakota Notes No. 13. North Dakota Geological Survey.dmr.nd.gov (opens in a new tab)
  4. Texas Beyond History (University of Texas at Austin). Gravels and lithic materials of the Texas coast (silicified wood).texasbeyondhistory.net (opens in a new tab)
  5. Virginia Department of Historic Resources, Lithics. Silicified Sandstone (page updated 4 April 2023; author not shown in the text opened).dhr.virginia.gov (opens in a new tab)
  6. Virginia Department of Historic Resources, Lithics. Silicified Mudstone (page updated 4 April 2023; author not shown in the text opened).dhr.virginia.gov (opens in a new tab)
  7. Mississippi Department of Environmental Quality, Office of Geology. Lithic Materials (web page; updated December 2023).mdeq.ms.gov (opens in a new tab)

Named stones of this kind

All materials