Pisolite
“Pea-sized stone pearls”
Pisolite is a sedimentary rock composed of rounded grains called pisoids — spherical concretions larger than 2 mm (bigger than ooids) built up from concentric layers of minerals around a nucleus. They form in caves, hot springs, soils, and shallow marine environments through repeated mineral precipitation.
calcite, aragonite, iron oxides (in lateritic pisolites), aluminum hydroxides, variable cement
Carlsbad Caverns (New Mexico, USA), Cappadocia (Turkey), laterite soils of Western Australia, hot springs worldwide
3-5 (varies by composition)
In the bauxite deposits of Western Australia, iron-aluminum pisolites litter the ground surface like scattered marbles — they're so abundant that their presence is used as a prospecting tool for finding ore beneath.
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