page_title: Calcite rafts
section_title: Concrete leachate drops
hierarchical_section_title: Calcite rafts / Concrete leachate drops
caption_attribution_description: English: Lattice work of calcite rafts have formed on slow dripping calthemite straw drop
context_page_description: Calcite crystals form on the surface of quiescent bodies of water, even when the bulk water is not supersaturated with respect to calcium carbonate. The crystals grow, attach to one other and appear to be floating rafts of a white, opaque material. The floating materials have been referred to as calcite rafts or "leopard spots".
context_section_description: Micro calcite rafts have been observed on (soda) straw stalactites solution drops suspended beneath concrete structures. These secondary deposits which form outside the cave environment, are known as calthemites. They are derived from concrete, lime or mortar, and mimic the shapes and forms of speleothems created in caves.
  The micro rafts which form on the surface of hyperalkaline leachate solution drips are typically about 0.5 mm in size when visible to the naked eye, and appear on the drip's surface after it has been suspended for greater than ≈5 minutes. The chemical reaction which creates the rafts, involves carbon dioxide (CO₂) being absorbed (diffusing) into solution from the atmosphere and calcium carbonate (CaCO₃) precipitates as rafts or deposited as a stalagmite, stalactite or flowstone. This chemistry is very different to that which creates speleothems in caves.
  Internal water pulses from the straw (into the drop) and air movement around the suspended solution drop, can cause the rafts to spin swiftly around the drop surface. If there is almost no air movement around the suspended drop, then after approximately 12 minutes or more, the micro rafts may join up and form a latticework, which covers the entire drop surface. If the solution drop hangs too long on the straw (≈ >30 minutes), it may completely calcify over and block the calthemite straw tip.
caption: Lattice work or calcite rafts on a calthemite (soda) straw stalactite drop
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