The NSS Bulletin - ISSN 1090-6924
Volume 44 Number 1: 15-19 - January 1982

A publication of the National Speleological Society

Origin of Black Deposits in Caves
Carol A. Hill


Black deposits in caves can be composed of several different materials; manganese minerals, soot, guano, tar, and humate are some which are described in this paper.

Manganese occurs as black coatings on cave walls and stream clasts, as a stain on speleothems, or as black fill deposits. Several different manganese minerals have been identified in black deposits: birnessite, romanechite (psilometane) rancieite, lithiophorite, and todorokite. A manganese origin can be verified by a simple chemical test.

Soot from torches and lanterns accumulates on the ceiling and uppers walls of a cave. In Black Cave, Guadalupe Mountains, New Mexico, soot from a surface fire has been transported into the cave by vadose water. Evidence for guano fires is ash within floor guano deposits.

Dark brown to black guano deposits are recognizable by their smell, pelletal nature, and the presence of bones, hair, or insects; if decomposed, the guano has a high phosphate content.

Blackish organic humate and other carbonaceous matter in caves must be identified on the basis of chemical tests, X-ray diffration techniques, and infrared absorption spectra analysis.

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