Crystals in geological processes. Part 1. Morphology and development of crystals

elective courses

Basic knowledge in the field of dynamic geology (physical geology).

The lecture presents the basic modern knowledge about the genesis and development of crystals from a geological point of view, focusing on natural crystals, i.e. crystalline minerals. The nucleation of crystals, their growth as well as transformations and deformations that occur in various geological environments will be discussed. First of all, the internal and external (morphological) features of the crystals will be characterized that permit to restore the history of their development and reconstruct crystallization conditions and environment. This lecture focuses mainly on single crystalline individuals, to a lesser extent on their intergrowths, twinnings, and selected aggregates.

The supplement/continuation of the lecture is its second part devoted to the development of more complex aggregates and accumulations of many crystals (Lecture entitled „Crystals in geological processes. Part 2. Aggregates and accumulations of crystals”).

General characteristics of crystals and crystallization processes. Periodic and aperiodic crystals. Natural quasicrystals. Natural colloidal crystals (precious opal). Nanominerals and mineral nanoparticles (their properties and significance). Megacrystals (the largest minerals) and the conditions of their development. Morphology and internal structure of crystals. Space lattice and crystal lattice. Point, line defects (edge, screw and mixed dislocations), flat, and volume defects. Faceted and non-faceted crystals. Crystals as grains in metallurgy. Crystallites. Forms and combinations of crystallographic forms. Form of growth, stable form of growth, equilibrium form. Theory of periodic bond chains (Hartman-Perdok) and crystal morphology. Real and ideal crystals. Crystallization from gas phase, solutions and liquid alloys (magma). Driving force for crystallization. Methods for obtaining synthetic crystals and minerals. Natural crystallization. Theories of crystal growth. Mechanisms of crystal growth and crystal morphology in low and high supersaturation and supercooling. Atomically-rough and smooth crystallization front. Dislocations and crystal growth. Generation of dislocations and their reproduction. Growth and post-growth dislocations. Examination of dislocations in minerals. Normal and layered growth of crystal faces. Elemental (monomolecular) steps and macrosteps, flow and bundling of steps. Creation of elementary steps by two- and three-dimensional nucleation. Dislocation (spiral) mechanism of continuous growth. Nucleation of crystals. Classic and non-classical nucleation theories. Subcritical, critical and supercritical nucleus. Pre-nucleation clusters. Primary (homo- and heterogeneous) and secondary nucleation. The causative (driving) forces of nucleation: supersaturation (in solution) and undercooling (in alloy). Nucleation of biominerals. Crystal nucleation in natural environments. Stages of crystallization from solutions: pre-nucleation stage (induction time), nucleation stage, and growth stage. Undersaturated, saturated and supersaturated solutions. Metastable state. Crystallization from solution by evaporation and cooling. Crystallization by chemical reaction (precipitation) and by changing the chemical composition (salting out). Examples from natural environments. Crystallization by cooling of the alloy (magma). Liquidus. Solidus. Supercooling and degree of supercooling. The nucleation rate and growth rate of crystals in the solidifying magma and the texture of igneous rocks. Ostwald ripening. Distributions of crystal sizes in rocks (distributions with Ostwald ripening and others; examples of interpretation). Factors affecting the course of crystallization and the rate of crystal growth. Anti-skeletal and skeletal growth. Relief (microtopography) of crystal faces and growth accessories. Dislocation and non-dislocation growth hills and pits. Growth centers and spirals. Lines of growth layers. Vicinal faces and pyramids. Striations of the faces. Traces of dissolution and etch figures (etch pits). Examples from the world of minerals. Subcrystals. Parquette crystal surfaces. Block (mosaic) structure of crystals. Crystallites. Lineage structure and its development. Block boundaries (boundaries of subcrystals). Growth pyramids (growth sectors) and growth zones. Growth zoning. Types of zoning. Compositional zoning. Diffusional zoning and its development. Concentric, sector and intrasector zoning. Oscillatory zoning and its genesis. Examples from the world of minerals. Zoning of feldspar: normal, inverse and oscillatory zoning. Patch zoning. Hourglass structure (chiastolite, star sapphire and others). Inclusions in crystals (solid, liquid, gas, primary and secondary) inclusions and their use in geological studies. Examples of application of inclusion analysis to interpretation of crystallization conditions. Melt inclusions in crystalline rocks. Crystal morphology and environmental conditions. Influence of supersaturation, temperature, pH, foreign admixtures on crystal morphology. Adsorption of admixtures on crystal faces; palisade of Cabrera. Morphological evolution of growing crystals and its causes. Selective adsorption as a mechanism inhibiting the growth of specific faces and generating changes in crystal morphology. Development of a particular polymorph phase under the influence of specific admixtures. Growth morphodromes (crystallogenetic diagrams). Methods of their construction and examples from the world of minerals. The concept of mineral typomorphism. Index minerals. Critical minerals. Typomorphic minerals. Typomorphic features (properties, indicators). Morphological typomorphism. Examples of typomorphic mineral development (zircon, feldspar, pyrite, fluorite and others). Typomorphism in geological exploration. Exploratory crystallomorphology. Asymmetric development crystals and its causes. Dislocations and accelerated growth of faces. Asymmetrical crystal development in solidifying alloys due to heterogeneous cooling. Concentration streams around a growing and dissolved crystal. "Geotropism" of natural crystals and its causes. Orientation of crystals in mineral veins - an example of quartz. Influence of solution flow direction on crystal morphology. Crystals growing in streams of mineralizing solutions. Examples from the world of minerals. Analysis of brine palecurrents based on the orientation of gypsum crystals in the Carpathian Foredeep basin. Precipitation and growth of floating crystals on the surface of the solution. Crystal boats and rafts; examples (halite, calcite, etc.). Crystals with curved faces. Somatoids. Effect of adsorption, dissolution and igneous corrosion on the formation of curved faces. Examples from the world of minerals (lenticular gypsum, diamonds). Twisted crystals, their features and origin; examples (saddle dolomite, radiaxial calcite, twisted quartz, gypsum). Skeletal crystals, vertex and edge development (skeletal growth, Berg effect). Anti-skeletal crystals. Two- and three-dimensional dendrites, faceted and non-faceted dendrites. Conditions and mechanisms of dendrite growth. Forehead and dendrite branch development. Factors controlling the shape of dendrites, the role of diffusion. Examples of dendrites from the world of minerals. Whiskers and needle (fibrous) crystals. Metal, non-metal and mineral whiskers. Mechanisms of needle crystals growth. Growth at the base and at the top of the crystal (examples from natural environments). Splitting of growing crystals (examples of calcite and gypum). Deformations, destruction and transformation of natural crystals. Dissolution of crystals, negative crystals. Synsedimentary dissolution of salt minerals, dissolution surfaces (gypsum, halite). Structural transformations of mineral crystals. Compaction and tectonic deformations and cracks. Deformation caused by impacts (shocked quartz). Regular intergrowths of the same crystal phase. Parallel and non-parallel crystal intergrowths. Definitions of twins and their symmetry. Growth, transformation and glide (mechanical) twins - their morphology and genesis. Penetration and contact twins. Double, triple and multiple (polisynthetic) twinning. Origin and rules of development of growth twins (the role of supersaturation and admixtures). Nucleation twins. Theory of original composition plane. Synneusis. Review of characteristic mineral twins (rutile, staurolite, aragonite, cerusite, chrysoberyl and others). Transformational quartz twins. Polysynthetic feldspar, calcite and dolomite twins. Swallowtail gypsum twins growing on the substrate, Mottura's rule. Regular intergrowths of crystals of different phases. Epitaxy and epitaxial intergrowths. Graphoepitaxy. Feldspar and quartz epitaxy. Graphic granite. Myrmekite. Examples of epitaxy from various environments. Topotaxy and topotactic intergrowths. Exsolution of solid solutions. Examples from the world of minerals. Pertites and antipertites. Widmanstätten figures. Growth of crystals surrounded by foreign bodies; incorparative, displacive and replacive growth. Crystallization force and pressure. Pseudomorphoses. Paramorphoses, metamictic crystals, exsolution pseudomorphoses, alteration pseudmorphoses, replacement pseudomorphoses (pleromorphs), and encrustation pseudomorphs (perimorphs). Examples of famous pseudomorphoses (glendonite, achtarandite and others). Crystals in living organisms. Biomineralization. Biominerals and organominerals. Controlled biological biomineralization (intra-, inter- and extracellular). Biologically induced biomineralization. Examples of biominerals (calcite, aragonite, magnetite, etc.). Experimental biomineralization. Biomimetic crystallization in material engineering. Crystals and chiral organic compounds. The hypothetical role of crystals in the creation of life on Earth.

The lecture teaches you to understand the processes of growth and transformation of natural crystals (minerals), and to recognize (interpret) the record of these processes in macroscopically visible morphological features and the internal structure of crystals and their intergrowths. The lecture teaches understanding of Polish and English-language scientific terminology.

The final test or oral colloquium checking the level of knowledge acquired during the lecture.

In the case of conducting classes remotely (On-line), assessment may be based on the assessment of self-prepared written works on a given topic.

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