text: Calcite rafts were first observed by Allison in 1923 on solution drops attached to concrete derived straw stalactites, and later by Ver Steeg. When the drip rate is ≥5 minutes between drops, calcium carbonate will have precipitated on the solution drop surface (at the end of a stalactite) to form calcite rafts visible to the naked eye (up to 0.5 mm across). If the drip rate is greater than ≈12 minutes between drops, and there is very little air movement, these rafts may join up and become a latticework of calcite rafts covering the drop surface. Significant air movement will cause the rafts to become scattered and spin turbulently around the drops surface. This turbulent movement of calcite rafts can cause some to shear off the drops surface tension and be pushed onto the outside of the straw stalactite, thus increasing the outside diameter and creating minute irregularities.