FORMATION OF CHERT (FLINT)
1. What is Chert (or Flint).
a. Chemical composition is Silicon and Oxygen, Silicon Dioxide, SiO2. or Silica.
b. Some of purest forms of silica originated from marine organisms, diatoms, etc.
c. Layers of silica accumulated (marine animals/plants) over time in some areas on
the ocean floor that exceed 300 feet.
2. Formation Theories.
a. Silica layers were covered by sediments resulted in high temperatures and
pressures. These conditions produced some of the sedimentary tabular type cherts.
b. Silica under high temperature and pressures, plus right ph, resulted in chert
dissolving back into solution, then precipitating out into tabular and nodular chert.
c. Silica in solution also formed into a gel, dehydrated into solid chert. This gel also
folded over onto itself resulting in various formations with fossils, etc.
d. In all probability, chert resulted from all of above plus others. The factors most
controlling types are temperature, pressure, ph, and other elements.
e. Low T and P near the surface produced the quartz crystals such as the Arkansas
type crystal. High T and P produced the chalcedony, molecular chain types.
f. Much is still not understood about chert formation, although the crystals can be
“grown” in the laboratory. Barbara Ludkhes’ manual, The Archaeologists Guide
to Flint and Chert”, is a good reference.
3. Silica outside the Marine Environment.
a. Chert is also located outside the marine environment such as volcanic areas. This
type is designated as obsidian or natural glass.
4. Chemical Elements in Chert.
a. A total of 76 elements have been identified in chert compounds.
b. Most common in order; Fe, Na, Zn, Ba, Rb and Cs, plus clays, carbonates, etc.
5. There is no agreed upon definition as to the difference between chert and flint, in any.