Abstract
The effects of temperature and degree of supersaturation (as controlled by temperature gradient) on the morphology of hydrothermally grown pyrite crystals were investigated over the temperature range from 250 to 500 °C. At a mean temperature of 250 °C and with low supersaturation (temperature gradient of 0.35 °C/cm over 8 cm), needles were produced by the screw-dislocation growth mechanism. As the temperature and/or degree of supersaturation increased (to a mean temperature of 450 °C and a temperature gradient of 4.6 °C/cm and higher over 8 cm), the sequence cube to octahedron to pyritohedron was produced. At extremely high degrees of supersaturation, which occurred during quenching, the growth mechanism shifted from being surface-controlled to diffusion-controlled, causing dendritic growth. Pyrite habit may be used to delineate relatively concentrated zones of nutrient-rich fluid flow.
