Non-equilibrium highly anisometric crystals and whiskers of galena

Abstract

Unusual irregular galena crystals and whiskers were found in close proximity in some druse cavities from the Gradishtc hydrothcrmal lead-zinc deposit in the Madan ore district, Bulgaria. The following crystal forms were observed: (1) straight thin [110] whiskers and thicker needles; (2) kinked whiskers; (3) curvilinear whiskers; (4) complex tortuous whiskers composed of segments with varying directions--[ll0], [1(30], [211], (5) thicker irregular elongated crystals. Combinations of these forms occur also. The detailed SEM study shows that all these formations are single crystals of extreme anisometricity, bounded by octahedral and cubic faces as well as by stepped surfaces of these forms. Surface structures such as longitudinal grooves, jagged edges, striations, pits, etc., are abundant.It is assumed that these highly non-equilibrium crystals with large surface areas were formed through rapid directed growth from highly supersaturated solutions under a diffusional regime. Such special environments arose in the ore veins as a result of tectonic shocks leading locally to a drastic volume increase and P and 7" decrease in the solutions.

MORPHOLOGY, COMPOSITION AND STRUCTURE OF LOW-TEMPERATURE P4/nnc HIGH-FLUORINE VESUVIANITE WHISKERS FROM POLAR YAKUTIA, RUSSIA

“…As will be shown in this study, acicular vesuvianite displays zonal growth, whereas whiskers are homogeneous. The appearance of natural whiskers depends on growth conditions and mechanism of crystal growth (Maleev 1971, Bonev 1993, Bonev et al 1985, Galuskin & Winiarski 1997. Whiskers of pyroxenes and amphiboles are well known, and their one-dimensional growth is generally attributed to polymerization of SiO 4 tetrahedra forming chains or bands (Maleev 1971, Galuskin & Mokhov 1991, Armbruster et al 2000c, 2002b.…”

Synthesis and growth mechanism of whisker‐like Mg 2 B 2 O 5 crystals by an easy and environmentally hospitable non‐aqueous ionic liquid method

“…Meanwhile, the experiments clearly showed that the reaction temperature was increased by around 80°C abruptly (from 850 to 930°C) in a short time owing to the carbonisation of the surfactant NP-9. The increase in reaction temperature may produce a highly non-equilibrium condition and supersaturated solution [29], which can directly lead to the growth of whisker-like Mg 2 B 2 O 5 crystals. The growth mechanism of whisker-like Mg 2 B 2 O 5 crystals is similar to the growth process of fine needle-like galena skeletons from highly supersaturated solutions [29].…”

Single crystal galena pillars as highly anisometric dissolution forms

“…In their morphological characteristics the rounded galena pillars contrast with the highly anisometric needle-like crystals and whiskers formed in growth processes (Bonev, 1993). These growth forms are entirely bounded by smooth and striated crystal faces, and follow crystallographic directions determined by the existing faceting.…”

“…It is particularly surprising to find them in a highly symmetrical material such as hexoctahedral PbS. However, extremely anisometric crystals and whiskers of galena can arise under suitable hydrothermal conditions as non-equilibrium growth forms (Bonev, 1993).…”