How are Liesegang rings formed?
Liesegang rings may form from the chemical segregation of iron oxides and other minerals during weathering. A process of precipitation known as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle is known by the geologic community as a probable mechanism for Liesegang ring formation in sedimentary rocks.
What causes rings in rocks?
When rainwater filters through the ground in arid regions, it dissolves calcium from soils, which can react with carbon dioxide to form the mineral calcite. This calcite precipitates on rocks ranging in size from pebbles to boulders, coating them with white growth-ring-like layers called pedothems.
Is Sandstone acidic or alkaline?
Sandstones contain much silica and so give rise to neutral or slightly acid soils, where the pH can be as low as 3.5.
What is the most common material found in sandstone?
sand
Whilst sand is the most common element found in sandstone (hence the name), there can often me other materials found in it such as cement and matrix. Cement located within the stone is usually comprised of quartz, calcium carbonate or iron oxide.
What is Adenomatoid odontogenic tumor?
Adenomatoid odontogenic tumor (AOT) is a well-recognised slow growing benign tumor derived from complex system of dental lamina or its remnants. This lesion is categorised into three variants of which the more common variant is follicular type which is often mistaken for dentigerous cyst.
Is Sandstone soft or hard?
Most sandstones are made up largely of quartz grains, because quartz is a very hard and chemically-resistant mineral. Quartzite is a name given to very hard, pure quartz sandstones. Many sandstones contain some grains of other minerals like calcite, clay, or mica.
What is the mechanism for the formation of Liesegang rings?
The precise mechanism from which Liesegang rings form is not entirely known and is still under research, however there is a precipitation process that is thought to be the catalyst for Liesegang ring formation referred to as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle.
Who was the first person to discover Liesegang banding?
In 1896, a German Chemist named Raphael E. Liesegang first described Liesegang banding in his observations from the results of an experiment, and Wilhelm Ostwald provided the earliest explanation for the phenomenon.
Where are Liesegang rings found in sedimentary rocks?
Though Liesegang rings are considered a frequent occurrence in sedimentary rocks, rings composed of iron oxide can also occur in permeable igneous and metamorphic rocks that have been chemically weathered.
Where are the Liesegang rings found in South Africa?
Liesegang and successive other workers observed the behavior of precipitates forming rings in sedimentary rocks, hence these features became known as Liesegang rings. A close view of a Liesegang ring present on a natural arch of sandstone, found at a beach near Khayelitsha, South Africa.