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 active danger deposits geothermal geothermally hot natural new zealand Rotorua sulfur sulphur toxic vapor vapour Australia Champagne cloud crystals Lacustrine plain lake landscape pink sky Geological phenomenon outcrop yellow accumulated accumulations aged calcium-carbonate caving ceilings coloring colouring columns compounds crystallisation crystallization crystallize distinctive edges forms geological geology icicle-like limestone mineral-deposits minerals old Particles pointed shape shaped shapes slow slow-growth slowly smooth speleology speleothems spelunker spelunkering stalactites subterranean surface surfaces textures Underground unusual candle-shapes caves colours crystallise edge floors pillars Singapore stalagmites white