Spongolite
“Stone made of ancient sponge needles”
Spongolite is a siliceous sedimentary rock composed largely of the tiny silica spicules — skeletal needles — of marine sponges. When sponge populations flourished on ancient sea floors, their accumulated spicules formed thick deposits that lithified into this lightweight, porous rock.
siliceous sponge spicules (opal), microcrystalline quartz, calcite, clay minerals, glauconite
Mount Gambier (South Australia), Murray Basin (Australia), southern England (Upper Greensand), Cretaceous deposits worldwide
3-5
In southern Australia, spongolite was quarried as a building stone because it's lightweight, easy to cut when wet, and hardens on exposure to air — several heritage buildings in Mount Gambier are made of it.
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