Name: derived from its occurrence at the Achates River in southwestern Sicily.
Clades: variety of
Chalcedony; uartzes;
Tectosilicates;
Silicates;
Lapidae.
Chemical: SiO2.
Crystal system: Trigonal or Monoclinic.
Color: colorless, gray, red, white, any color due to embedded minerals, multicolored specimen not uncommon.
Lustre: waxy, dull.
Hardness: 6½ to 7.
Specific gravity: 2.6.