Oolites and pisolites

In the Czech Republic, in the famous resort of Karlovy Vary, so-called "pea stones" form in hot springs. Their structure can cause admiration: they are geometrically regular "pea" aragonite (CaCO3) with a diameter of 2-5 mm, cemented with each other. Small peas are oolites, and larger peas are pisoliths. Oolites and pizolites are formed in the mobile aquatic environment of carbonic mineral "brook" or in caves. A grain of calcium, aragonite, etc., begins to grow on a grain of sand that serves as the center of crystallization, etc. The grit freely rolls along the bottom, and the "shirt" of the mineral increases evenly, and the spherical shell can have its own color shade. At some stage these pea-oolites are cemented. Thus, the "pea stone" is obtained.

Oolites and pizolites are formed in the mobile aquatic environment of carbonic mineral brook or in caves

By the way, calcite-aragonite pearls also have a similar oolithic structure. They grow inside the shells of pearl mussels. Of commercial importance are, for example, the two-folded mollusks of pipktada, common in shallow waters of the Indian and Pacific oceans. The largest of the known pearls on earth was found in 1934 on the Philippine Islands in the shell of a giant tridacna. It was 24 cm long, 14 cm across and weighed about 6 kg!

Oolites and pizolites are also found in ore veins in the depths of the earth or in sedimentary rocks on the seabed. Such forms of crystallization are known for magnetite, hematite, sphalerite, pyrolusite.

Each of you has already many times found silicon or chalcedony agate nodules-concretions. All of them are composed of fine-grained quartz or its fine-grained variety - chalcedony. If you make a thin preparation from a flint (a transparent section), then under the microscope you will see a picture of an impressive originality: the chalcedony fibers are distributed in space not arbitrarily, but as beams in a dandelion - in all directions from numerous centers. The rays in them closely adjoin each other. These are spherulites.

Spherolites originate on a grain of sand, a mineral fragment or on a "split" crystal of the same mineral. In free space they can take the form of geometrically regular balls.