Characteristics of crystal growth in nature as seen from the morphology of mineral crystals

Abstract

Crystal growth from solution phases is most universal and important in natural crystallization. Its essential features are : 1) mass transfer and 2) interaction between solid and liquid phases, in addition to lower growth temperatures, and, in general, smoother solid-liquid interfaces, as compared to melt growth. The morphology of crystals changes depending on the degree of supersaturation σ in solution growth, and there are two transitional supersaturations σ* and σ**, where transitions from bulky to hopper, and from hopper to dendritic morphologies occur, respectively. Changes of morphology during crystal growth (internal morphology) may be analysed on this basis. The σ* and σ** vary depending on materials and environmental conditions. Surface microtopographies of crystal faces of natural crystals are analysed using α-factors and γ, Δμ/kT, and compared with laboratorically synthesized crystals, and characteristics of natural crystallization are discussed. Growth under metamorphic and metasomatic conditions are also analysed based on the surface microtopographic observations.