Lowry Mall Current Container Display
University of Missouri Department of Geological Sciences
Rock type: Iron Ore
Location: Pilot Knob, MO
This rock is made of layers that alternate in grain size and composition from coarser-grained and
quartz-rich to finer-grained and hematite-rich. Hematite (Fe2O3) is an iron oxide that can appear
red or grey. The grain size changes are most obvious on a rough face, while the color changes
are most obvious on a smooth cut face. Preserved hexagonal mudcracks suggest that the rock
formed from sediment on the floor of a lake that periodically dried out. Ideas for the formation
of the hematite in this rock include (i) infiltration of sandstone by iron-rich fluids, replacing other
minerals with hematite, and (ii) deposition in a volcanic lake, where the hematite precipitated
directly from hot volcanic fluids discharged into the lake at a hot spring. The original rock is
about 1.47 billion years old. Quarrying at Pilot Knob began in 1835 and ended in the 1920’s.
A subsurface deposit of magnetite (Fe3O4) was mined from 1965 until the 1980’s.
Photo by Alan Whittington, MU Geology
MU Geology Department