to moonmilk.com
| |
When we named this site moonmilk, we didn't know that the name had already been used for centuries to describe a rich organic goo found in caves. To search the web for information about cave moonmilk without interference from moonmilk.com, try this Google search:
Search by Google
| |
Moonmilk
Laboratory cultures made from the water found on some cave deposits reveal the presence of bacteria and other microorganisms that may play a part in the construction of certain calcareous mineral deposits and in the disintegration of the limestone wall rock.
Microorganisms have been shown, for example, to play a major role in the origin of a curious cave material known as moonmilk. This is a soft, white, claylike substance present on the walls of many caves. Its name comes from the German-speaking part of Switzerland, where in the 16th Century people called it Monmilch, Mon being an old spelling for Mond, the present German word for moon. The people then believed that this underground white material was formed by the rays of the Moon. In the 16th Century, it was generally thought that the nightime dew was produced by the Moon. At that time, light from celestial bodies was believed to gain substance as it passed through rock, thereby producing metallic ores, for example, gold from the Sun and silver (and moonmilk) from the Moon.
The mineralogy of moonmilk has been intensively studied in Europe and North America during the past 30 years. We now know that the microscopic grains in the moonmilk of limestone caves consist mainly of calcite. But in relatively warm caves where the wall rock contains appreciable quantities of magnesium as a constiuent of the mineral dolomite, the grains may consist of any of the following magnesium minerals: hydromagnesite, magnesite, huntite, nesquehonite, and dolomite.
When the mineral constituents of moonmilk are removed by dissolving it in a weak acid, an abundant organic residue remains, which consists chiefly of such bacteria as Macromonas bipunctata, along with actinomycetes and algae. This microflora may assist in breaking down the minerals of the wall rock, and it aids in their conversion to the solids contained in the moonmilk.
The larger mineral bodies in calcite moonmilk have a distinctive surface sculpture that can be seen under the scanning electron microscope. The bodies consist of rods of calcite with an average size of 1 x 8 micrometers. A diagonal grain is impressed on the surfaces of the rods, and parallel ridges commonly trend along the lengths of the rods superimposed on the diagonal grain. The combined effect produces bodies somewhat resembling ears of corn.
The diagonal grain is aligned with the crystal structure, as can be seen through an optical microscope with polarized light. Because the crystal structure of calcite normally parallels the long dimension of calcite crystals, the grains in calcite moonmilk were once erroneously identified and named as a separate new mineral, "lublinite."
In many samples, the rods are enmeshed in a net of calcite filaments about 0.1 micrometer in width. These filaments are believed to have been associated with microbes that serve as nuclei for growth of the calcite bodies. An inclined crystal face of a seed crystal is nucleated by the microorganism and subsequent growth leads to the unusual crystal orientation and surface sculpture of the moonmilk grains.
Most moonmilk occurs where water may reasonably be inferred to move through the substance to its surface where deposition takes place by loss of carbon dioxide. The life processes of individual microorganisms cause a microvariation of the chemical environment that leads to deposition of discrete mineral grains, rather than to a more solid speleothem such as cave coral.
In a specimen of fresh calcite moonmilk from Caverns of Sonora, Texas, imaged by transmission electron microscopy, several of the thinnest (and shortest) mineral filaments have round organic bodies 0.1 micrometers in diameter at one end. We suggest that this offers an explanation for the small size of moonmilk grains. The organism nucleates the rod from one end only, until it divides. Subsequent thickening and sculpturing of the rod then takes place mainly by inorganic mineral overgrowth.
More research is needed to determine the energy source of the microorganisms in moonmilk. The snow-white rather than brown color of most moonmilk suggests that oxidation of iron is not the source.
In 1994, Rudolph Reinbacher studied freshly forming moonmilk in Mondmilchloch, Switzerland, the type locality for the substance. The moonmilk there is calcite with a color (wet) in the Munsel color system of very pale orange (10YR8/2). A sample stored in a jar in dim light for several months acquired brown, gray, and green spots, presumably from microbial contamination. This growth proves that nutrients remained in the sample and suggests that soluble organic compounds from the soil provide the energy for the microorganisms that control the growth of this strange substance.
George W. Moore
| |