abstract accretions accumulated accumulations coloration coloring colors colouring colours columns crystallisation crystallise crystallization crystallize deposits distinctive edge edges formation forms glassy layered layers levels light shape shaped shapes slow slow-growth slowly smooth surface surfaces texture textures unusual aged calcium-carbonate candle-shapes caves ceilings floors icicle-like minerals old Particles pillars pointed Singapore Stalactite stalactites stalagmites subterranean white cave cavern caving compounds geological geology limestone mineral-deposits speleology speleothems spelunker spelunkering Underground bio-chemical-accretionary-structures cementation columnar cumulative-structures excretions formations formed forming fossils high-saline-levels lake living-fossils living-rocks microbialites microorganisms natural park rock-structure sedimentary-grains shallow-water stromatolite stromatoliths structures birth and growth death and decay inspiring inspiring nature nature nature photography outdoors mushrooms photography plants relaxing pictures scenery trees