Bull Volcanol (2005) 67(3): 268-280In the original online publication and the print version of this article, Tables 1 and 2 were unfortunately omitted. We apologise for this error. The tables are printed below.The online version of the original article can be found at http://dx
Among the series of eruptions at Miyakejima volcano in 2000, the largest summit explosion occurred on 18 August 2000. During this explosion, vesiculated bombs and lapilli having cauliflower-like shapes were ejected as essential products. Petrological observation and chemical analyses of the essential ejecta and melt inclusions were carried out in order to investigate magma ascent and eruption processes. SEM images indicate that the essential bombs and lapilli have similar textures, which have many tiny bubbles, crystal-rich and glass-poor groundmass and microphenocrysts of plagioclase, augite and olivine. Black ash particles, which compose 40% of the air-fall ash from the explosion, also have similar textures to the essential bombs. Whole-rock analyses show that the chemical composition of all essential ejecta is basaltic (SiO 2 =51-52 wt%). Chemical analyses of melt inclusions in plagioclase and olivine phenocrysts indicate that melt in the magma had 0.9-1.9 wt% H 2 O, <0.011 wt% CO 2 , 0.04-0.17 wt% S and 0.
Mineralogical processes taking place close to equilibrium, or with very slow kinetics, are difficult to quantify precisely. The determination of ultraslow dissolution/precipitation rates would reveal characteristic timing associated with these processes that are important at geological scale. We have designed an advanced high-resolution white-beam phase-shift interferometry microscope to measure growth rates of crystals at very low supersaturation values. To test this technique, we have selected the giant gypsum crystals of Naica ore mines in Chihuahua, Mexico, a challenging subject in mineral formation. They are thought to form by a self-feeding mechanism driven by solution-mediated anhydritegypsum phase transition, and therefore they must be the result of an extremely slow crystallization process close to equilibrium. To calculate the formation time of these crystals we have measured the growth rates of the f010g face of gypsum growing from current Naica waters at different temperatures. The slowest measurable growth rate was found at 55°C, 1.4 AE 0.2 × 10 −5 nm∕s, the slowest directly measured normal growth rate for any crystal growth process. At higher temperatures, growth rates increase exponentially because of decreasing gypsum solubility and higher kinetic coefficient. At 50°C neither growth nor dissolution was observed indicating that growth of giant crystals of gypsum occurred at Naica between 58°C (gypsum/anhydrite transition temperature) and the current temperature of Naica waters, confirming formation temperatures determined from fluid inclusion studies. Our results demonstrate the usefulness of applying advanced optical techniques in laboratory experiments to gain a better understanding of crystal growth processes occurring at a geological timescale.phase shifting interferometry | mineral growth D uring the last decade, the field of mineral growth has experienced important advances in analytical instrumentation (1). The development of state-of-the-art methods for nanometric observation, such as high-resolution atomic force microscopy (2), or advanced optical microscopy techniques like laser confocal differential interference contrast microscopy (3) and phase-shift interferometry (4, 5), have allowed the study at nanoscopic levels of the different growth mechanisms exhibited by crystals, emphasizing the direct relation between the morphology and the growth processes taking place on each crystal face. For example, the application of in situ nanoscale observation of calcite crystal growth in the lab have revealed the microscopic causes of the large morphological variety exhibited by natural occurring calcite crystals (6-8). These, and other works (9-11) have demonstrated the power of laboratory crystal growth studies for sharpening the picture of crystallization occurring in nature.Recently, a very striking crystal growth problem in earth sciences has emerged: the existence of giant crystals of gypsum (CaSO 4 :2H 2 O), in particular those found in the range of Naica, Mexico (12, 13). Large gypsum cryst...
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