[Solved] What have been some of the significant achievements of the Clean Air Act? Columnar Joints: Natural formations resulting from the cooling and cracking of volcanic rock into nearly hexagonal columns. Finely Crystalline: Describes a rock texture that consists of small, closely-packed crystals not easily visible to the naked eye. Calcite: A common mineral form of calcium carbonate, critical in the formation of limestone and marble, and involved in many geological processes. Metamorphosed Fossils: Fossils that have undergone metamorphism, altering their original form and composition due to heat and pressure.