EUHEDRAL HYDROTHERMAL QUARTZ: QUANTIFYING GROWTH TIMES AND VISUALIZING THE MORPHOLOGIC EVOLUTION OF NATURAL CRYSTALS

Quartz crystals formed in hydrothermal environments contain hydrous impurities that were trapped in their crystal lattice during growth. The abundances of trace constituents reflect the physical and chemical conditions present during mineral growth. High-resolution micro-FTIR spectroscopy allows for quantitative determination of the abundance and internal distribution of hydrous chemical constituents. We show that variations in impurity concentrations serve to delineate sector zones within natural crystals; order-of-magnitude differences across sharp boundaries distinguish clearly regions within crystals that correspond to growth from specific rhombohedral and prism faces. We present detailed studies of crystals from different hydrothermal environments that show varying histories of crystal development.

Diffusion profiles within individual crystals offer particularly valuable insights into the process of euhedral quartz crystallization. Detailed IR profiles reveal that some natural crystals experienced variable soaking times at elevated temperatures for prolonged durations, whilst others were quenched rapidly immediately following their formation. Progressive decreases in the amount of diffusion observed with increasing height up the c-axis provides a measure of the duration of post-crystallization soaking for successive levels within the crystal. Our results on cm-sized natural hydrothermal crystals constrain their growth times from month to decades-long timescales. In addition, we present a visual simulation written in Java Programming Language that illustrates the morphologic evolution of quartz crystals as they grow from hydrothermal solution. The simulation illustrates how concurrent growth on different crystal faces leads to chemically distinguishable sector zones inside single crystals. The program utilizes Java Bindings for OpenGL to render the evolving crystal and can be accessed on the internet for classroom display using Java webstart technology.