Tripoli occurs in the vicinity of Seneca, Newton County, Missouri. It is
a light-weight, porous, white to creamy, siliceous rock, which may be
scratched because of its softness. Tripoli represents the porous
insoluble residue of an earlier rock, which was composed of skeletal
insoluble silica and interstitial soluble calcium carbonate (calcite),
the latter having been dissolved away by ground water. Tripoli has a
chalky appearance but is totally unlike chalk chemically. Tripoli is
nearly pure silica, whereas chalk is calcium carbonate. Any tripoli-like
rock found in Missouri outside the region of tripoli mines is likely to
be a fragment of weathered chert which is described above.
Tripoli has been used as an abrasive, a polishing agent, a parting
material in molding sand, and a filter rock.