Bill's Hematite Cone Page

My wife and I both got our geology degrees from what was West texas State University in Canyon Texas, now WT A&M.  Being close to Palo Duro Canyon we spent a lot of time there.Geological and meteoric processes have produced several interesting rock types in the canyon.  Near the top a band of opal  is pretty easy to find at the base of the Ogallalla.  Most of the way down the canyon slopes the Tecovis formation produces a lot of concretions, many hollow.  These geodes contain quartz crystals, calcite or sometimes celestite.  Other more rare minerals turn up occasionally.

The most interesting rock in my opinion is the cone shaped concretions forming in the upper Trujillo.  These are hematite cemented sandstone.  They are distributed only very locally, requiring just the right sedimentary, diagenetic, erosional, and now, meteoric conditions.  They are striking looking geochemical and geomorphic products of the canyon worth some notice.  These hematite cones vary from a half-inch in size ot over three feet long.  Unfortunately, after three decades I have been unable to relocate those larger than two feet in length.  Many are about 6 inches as this one.  Some, such as this one are perfect geometric cones.  Large cones such as this one usually break to pieces on weathering out.  The angles of the cones varies from about 10 degrees to about 80 degrees, presumabily dependent on the vertical permiability of the sandstone.  Internally they are nested cone shaped hematite cemented zones within the parent sandstone, such as seen here.

Some requirements for their occurance are;
1. Erosion of the overlying Ogallalla and uppermost Trujillo sandstone.
2. Preferrably 50 yards or more of erosion back from the overlying beds, presumably for many centuries of exposure to rainwater.
3.Presence of fine to medium grained sandstone between the the first Trujillo sandstone and the massive cliff forming Trujillo sandstones for the cones to form in.
4. South facing exposure is good.  Timber Mesa and many other sites have no cones on the north or east sides even when sandstone occurs in the proper stratigraphic location.
5. Some loci for meteoric iron precipitation.  This is probably weathering lignite and pyrite from plant fossils which are actually preserved only rarely.  Here is a picture of fossil material from the cone-bearing bed.  Some of the fossil wood will burn when heated with a match but the material is saturated with pyrite and smells of sulphur when burned.  Hematite-lined casts of the fossil plants are sometimes present in the cone-bearing layer and often common in beds below the cone-bearing sandstone.

I have been mapping and photographing these cones for the last several years using a combined GIS and GPS method.    Both air photos and topo contours are very helpful in finding a suspected site.  Most sites are so rugged a planned route to the site must be loaded into a very long battery life GPS unit or the sites cannot be reached. Even then more than three liters of drinking water are usually needed.  The cone occurance tends to be in remote very rugged sites so they provide an excuse to hike in some very scenic places.  So far I've mapped them and their source beds at 1 meter accuracy from about ten sites covering many square miles and have about a half dozen suspected sites still to check.

Click here for a view of typical source sandstone.
Click here for a view of a "rhino horn"shaped cone.
Click here for a distribution map for one of the sites, Timber Mesa.
Click here to see what happens when the source sandstone is too silty.
Click here to see how the cone debris washes down from the source beds.
Click here for a scenic view along Timber Mesa.
Click here for a series of views of embedded cones of different sizes
Click here for petrography of the cones.
Click here for an article on detailed 3D distribution at one site.(large and requires Acrobat Reader)