color colors diamond element florecent formation fossil gem geod Mineral mineral deposit natural deposit ore phosphorus precious rock rocks stone stones texture cave cavern crystal deposit drip Stalactite water accumulated accumulations aged calcium-carbonate candle-shapes caves ceilings coloring colouring colours columns crystallisation crystallise crystallization crystallize deposits distinctive edge edges floors forms icicle-like minerals old Particles pillars pointed shape shaped shapes Singapore slow slow-growth slowly smooth stalactites stalagmites subterranean surface surfaces textures unusual white