Palo Duro Canyon typical in-situ hematite cone



Most hematite cones eventually weather out of  the rock intact.  When they do they litter the ground, looking like "rhino horns"
This one, occurring in medium grained sandstone, has a typical cone apex angle.  In very permiable clean sandstone they are
sometimes very narrow.  In dirty fine grained sandstone they usually are broader with a 45 to 90 degree apex.
Polished microscope sections and crossections show the hematite is deposited in concentric rings with most of the
hematite in the outer rings.  The hematite is deposited as a cement, it does not replace the sand grains themselves.