Wykształcenie kryształów galeny z „iłów witriolowych" w niecce bytomskiej .

Marek Michalik



In so-called Vitriol Clays of the Bytom Basin, galena occurs in the form of either single crystals, usually about 1 mm in size, or intergrowths.
Crystals cubic or cubooctahedral in shape are most common here. Simple forms include {100} and {111}, the first of which clearly predominates. The crystals often display underdeveloped corners and margins and various types of skeletal crystals are fairly common. Skeletal crystals are characterized by common free spaces delineated by walls parallel to {100}/or, sometimes, {100} and {111}. Crystals composed of a few zones display some changes in share of individual simple forms. Walls {111} are more numerous in outer zones. Some skeletal crystals are built of a number of layers perpendicularly growing on walls {100}.
Walls {100} are smooth and {111} - with triangular depressions. Walls of galena crystals usually display steps of various types. When high (0.0x mm high) and oriented perpendicularly to wall surface or overhanging it, the steps markedly influence development of crystals.
The development of crystals makes it possible to state that their crystallization has been proceeding through either two-dimensional nucleation (mechanism of the Kossel-Stranski theory), under conditions of marked differences in oversaturation of solution close to corners, margins and central parts of crystal walls, or by accretion (i. e. mechanism also connected with marked oversaturation of solution). Growth of skeletal crystals has been also facilitated by impeded diffusion in clay sediment environment and adsorption of various pollutions. Crystal wall overhanging steps, varying in size, indicate oscillatory changes in conditions of crystallization. However, the oscillations were insufficiently large to result in change in mechanism of growth. Isometric development of crystals indicates isotropic nature of environment of crystallization (immobile solution, plastic sediment).

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