Pisolite

Pisoid (Latin pisum " pea" ) is a round single grains in sedimentary rocks, which is formed by the deposition of thin mineral layers.

Demarcation

This term from the petrography has different meanings in the older literature. A common meaning refers to a non formed in the sea, ply, relatively large Kalkkorn (or even non- Kalkkorn ) with a core. Today this refers carbonate or non- carbonate grains, which are similar to ooids in their plant construction. However, they differ from other formation mechanisms, other educational spaces in the detailed structure and above all by their size ( usually a few millimeters to centimeters ) of ooids. Due to the ambiguity of the term, it is now common practice to refer the term " Pisoid " by a suitable combination specifically, the emergence involving such Höhlenpisoide, fluvial or lacustrine Calichepisoide and Pisoide.

Some authors describe with the term Pisoid also round Karbonatkörner, which are formed by algae. This Pisoide should, however, be correctly referred to as Onkoide or Rhodolite.

Definition

Pisoide are generally rounded, the structurally ooids like grains having a diameter of more than 2 mm (up to several centimeters). They have dense, often somewhat irregular layers around a core ( nucleus). The shape is controlled by the education center. Some Pisoide in continuously moving water show an increasing sphericity in the outer layers, eg Höhlenpisoide ( " cave pearls " ) in drip pans or Pisoide in hot springs. In contrast Pisoide that were formed in the weakly moving water have, often at a decreasing sphericity in the outer layers. Other Pisoide are asymmetric and form the top and bottom layers thicker; others are elongated sideways. Rare Pisoide are also connected to each other. They can be broken now and then encrusted again. The nuclei are usually lithoclasts, peloids, fragments of other Pisoide or cement crusts. Pisoide arise almost chemically pure by precipitation ( Höhlenpisoide, Pisoide in thermal springs ), but also with strong participation of microbial mats (eg Calichepisoide ).

Rocks, which consist predominantly of Pisoiden are called pisolites. German names for this are pea stone or aragonite, which terms are limited to Höhlenpisoide or Pisoide in thermal springs.

Occurrence

The Pisolith and pea stone deposits in Carlsbad have been described and discussed by Johann Wolfgang von Goethe in an essay. Other European deposits are located, among others in Lower Austria, Switzerland and France.