Erongo Mountains, Namibia * 5 x 6 x 3 cm Page 251: Calcite, Irai, Rio Grande do Sul, Brazil * 12.5 x 10 x...A CHANGING PLANET 11 Vanadinite, San Carlos district, Chihuahua, Mexico * 8 x 4 x 2 cm Mineral Species...nodules — named for their angular cavities — with calcite (see photo opposite). Crystal linings that survive...silicate minerals known collectively as zeolites. Calcite (septarian nodule), San Juan County, Utah, USA...means “changed form”). For instance, the small calcite crystals in the sedimentary rock limestone change |