Cave popcorn

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Cave popcorn with frostwork

Cave popcorn, or coralloids, are small nodes of calcite, aragonite or gypsum that form on surfaces in caves, especially limestone caves.[1][2] They are a common type of speleothem.[1][2]


Cave popcorn trays

The individual nodules of cave popcorn range in size from 5-20 mm and may be decorated by other speleothems especially aragonite needles or frostwork.[1][2] The nodules tend to grow in clusters on bedrock or the sides of other speleothems.[1] These clusters may terminate suddenly in either an upward or downward direction forming a stratographic layer.[1] When they terminate in a downward direction, they may appear as flat bottomed formations otherwise known as trays.[1]

Individual nodes of popcorn can assume a variety of shapes from round to flattened ear or button like shapes.[2]

The color of cave popcorn is usually white but various other colors are possible depending on the composition.[2]


Button cave popcorn

Cave popcorn can form by precipitation.[1] Water seeping through limestone walls or splashing onto them leaves deposits when CO2 loss causes its minerals to precipitate.[2] When formed in this way the resultant nodules have the characteristics of small balls of flowstone.[1]

Cave popcorn can also form by evaporation in which case it is chalky and white like edible popcorn.[1] In the right conditions, evaporative cave popcorn may grow on the windward side of the surface to which it is attached or appear on the edges of projecting surfaces.[1]

Alisadr Cave, Hamedan, Iran


  1. ^ a b c d e f g h i j Palmer, Arthur N. (2007). Cave Geology. Dayton, OH: CAVE BOOKS. p. 288. ISBN 978-0-939748-66-2. 
  2. ^ a b c d e f Hill, Carol; Forti, Paolo (1997). Cave Minerals of the World (Second Edition ed.). Huntsville, AL: National Speleological Society. pp. 59–61. ISBN 1-879961-07-5. 

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