Arkansas novaculite in the Hot Springs-Little Rock area exhibits the texture, in scan electron micrographs, of a thermally metamorphosed rock formed ostensibly from cryptocrystalline chert. The stratigraphic formation, named Arkansas Novaculite, grades from a metamorphic rock in central Arkansas to typical cryptocrystalline chert at Atoka, Oklahoma, 250 air-km west. The Bigfork chert behaves similarly. It appears desirable to restrict the term "novaculite" to a petrologic name for a thermally metamorphosed chert which shows polygonal, triple-point texture; Arkansas novaculite is the type occurrence. Quartz crystals 60 mu m in diameter yielding relatively very coarse texture are developed in novaculite within 100 m of Mesozoic intrusives, e.g., at Magnet Cove. Coarse texture, crystals 10-20 mu m in diameter, is widespread at Hot Springs and Little Rock quarries. Fine texture (metamorphic) which ranges down to 1 to 2 mu m, occurs in the western part of Trap Mountain, 12 air-km southwest of Hot Springs. Similar texture occurs in the Broken Bow, McCurtain County, Oklahoma, region. Incipient-metamorphic texture appears in the Potato Hills region, Oklahoma, but at Atoka, Arkansas "novaculite" is cryptocrystalline chert. Thermal metamorphism of chert from vulcanism yields novaculite. In Ouachita locales of intense structural deformation coarse-textured novaculite is developed. Whether deformation alone generates adequate heat to produce novaculite is uncertain. Novaculite may be a geologic clue to a hidden intrusion, a thermal ore deposit (e.g., the vanadium in Arkansas), or a source of geothermal energy.