Cave popcorn

Last updated
Cave popcorn with frostwork Popcorn-with-Frostwork.jpg
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]

Contents

Appearance

The individual nodules of cave popcorn range in size from 5 to 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 known as trays. [3] [1]

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

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

Formation

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]

On manmade structures (outside the cave environment)

Popcorn can also occur on concrete structures outside the cave environment; these are classified as calthemite coralloids. Calthemite coralloids also occur in "artificial caves", such as mines, railways, or vehicle tunnels where there is a source of lime, mortar, or cement from which the calcium ions can be leached.

Coralloids can form by a number of different methods in caves; however, the most common form on concrete is created when a hyperalkaline solution seeps from fine cracks. Due to solution evaporation, deposition of calcium carbonate occurs before any drop can form. The resulting coralloids are small and chalky with a cauliflower appearance.[ citation needed ]

References

  1. 1 2 3 4 5 6 7 8 9 10 Palmer, Arthur N. (2007). Cave Geology. Dayton, OH: Cave Books. p. 288. ISBN   978-0-939748-66-2.
  2. 1 2 3 4 5 6 Hill, Carol; Forti, Paolo (1997). Cave Minerals of the World (Second ed.). Huntsville, AL: National Speleological Society. pp. 59–61. ISBN   1-879961-07-5.
  3. ↑ "Trays". The Virtual Cave. National Speleological Society.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.