The Oligocene–Miocene deposits of the Asmari Formation are located in SW of the Zagros Mountains of Iran. The lower part of the Asmari Formation consists of an evaporite bed that is termed Basal Anhydrite. Seven sections from four different anticlines were selected and sampled for petrographic and mineralogical analyses .The petrographical examinations were carried out using an optical polarize...

Anhydrite (CaSO4) phenocrysts from Mount Pinatubo pumices show evidence of having responded dynamically to changing conditions prior to the June 15, 1991 climactic eruption. Micrometer-sized and smaller pyramidal surface growth features and lesser numbers of etch pits on anhydrite surfaces are documented by scanning electron microscopy. Chemical analyses indicate that the pyramids are a CaSO4 p...

Introduction: The shock behavior of calcite and gyp-sum is important in understanding the Cretaceous/Tertiary event and other terrestrial impacts that contain evaporite sediments in their targets. Most interest focuses on issues of devolatilization to quantify the production of CO 2 or SO 2 to better understand their role in generating a temporary atmosphere and its effects on climate and biota...

The internal surface area of hexagonal (soluble) primary anhydrite CaSO4 produced by dehydration of gypsum decreases by about 70 % when the anhydrite is successively subjected to rehydration and dehydration at room temperature in humid air and in vacuum respectively. In the rehydration step, the hemihydrate is formed; its dehydration yields secondary anhydrite. Additional hydration-dehydration ...

[1] We develop mathematical models to investigate anhydrite precipitation in hydrothermal recharge zones at ocean ridge axes. We first consider constant flow during hydrothermal recharge to estimate the depth, the depth interval over which anhydrite precipitation would occur, and the initial rate of porosity reduction. We find that the smaller the downward mass flux, the shallower and more broa...

Infrared spectroscopic investigations have shown that on the basis of changes in the v3 , S0 4 band which occur when calcium sulphate is heated from 400° to 1400 °C, there are two forms of insoluble anhydrite, designated as ß'and /?-CaS04 . /?'-CaS04 is metastable and is completely converted into /?-CaS04 by heating above 1000 °C. With longer heating periods this conversion can even take place ...

Anhydrite solubility in H2O–NaCl solutions was measured at 6–14 kbar, 600–800 C and NaCl mole fractions (XNaCl) of 0–0 3 in piston–cylinder apparatus. Solubilities were determined by weight changes of natural anhydrite in perforated Pt envelopes confined with fluid in larger Pt capsules. In initially pure H2O at 10 kbar and 800 C, CaSO4 concentration is low (0 03molal), though much larger than ...

Anhydrite (CaSO4) is a major component of evaporitic rocks and is currently forming in submarine hydrothermal fields, where its dissolution and precipitation plays a significant role in controlling porosity. Anhydrite also is a component of undesirable scale on heat transfer surfaces during desalinization and waste water treatments. Knowledge of the molecular processes that control anhydrite gr...

Discovery of abundant anhydrite (CaS04) and gypsum (CaS0+2HzO) in the otherwise carbonate sediments comprising the upper portion of the rocks contained within the Chicxulub impact crater has prompted research on the shock-induced vaporization of these minerals. We use a vaporization criterion determined by shock-induced entropy. We reanalyze the shock wave experiments of Yang [ 11. He shocked 3...