Olivine Phenocryst morphology with glass and mineral inclusions

<p>The x-ray micro computed-tomography (micro-CT) model of this olivine crystal was acquired on a 2010 GE phoenix v|tome|x s240 system using a 180 KV nanofocus transmission X-ray tube. The olivine was placed in a low density polyethylene pipette. To achieve the smallest voxel size (nominally 1.1 &micro;m), the sample was placed as close to the x-ray source as possible without collision (&lt;1mm). In preliminary scans, we determined that the sample was blurring due to thermal expansion from the X-ray source. To combat this we placed the sample in the X-ray beam ~30 minutes prior to acquiring images so that a steady state could be reached.&nbsp;To further reduce image blur and ensure a crisp x-ray images the primary electron beam was manually focused immediately prior to data acquisition. A low accelerating voltage (40 kV) and molybdenum x-ray target was chosen to enhance compositional contrast in the x-ray images. Detector acquisition timing (333 ms per image), and X-ray source current &nbsp;(325&nbsp;&micro;A) was optimized&nbsp;to reduce image noise in the densest part of the image while ensuring a total acquisition time under 1 hour. A thin (0.1 mm) copper filter was placed in front of the x-ray beam to attenuate the beam hardening effects of polychromatic x-ray sources in CT images. For each image used in the tomographic reconstruction four images were averaged to reduce signal noise.&nbsp; A total of 1200 images were acquired for the tomographic reconstruction, resulting in an angular step size of 0.3˚. X-ray images were reconstructed into computed tomography volumes using GE Phoenix Datos software (version 2.3.2), a median kernel filter (3x3) was applied to the images prior to reconstruction to reduce signal noise, a beam hardening correction was applied to reduce artifacts in the Feldkamp cone beam reconstruction algorithm.&nbsp;Volumetric data was segmented and animated using Volume Graphics VG Studio Max 3.4 as well as the Fiji distribution of ImageJ.</p> <p>The olivine grain is from the terminal scoria deposits of the 1932 eruption of Volc&aacute;n Quizapu, Chile. The grain demonstrates the complexities associated with studying olivine (green) and its inclusions (here melt inclusion (dark red)&nbsp;with vapor bubble (teal) and oxide inclusion (yellow)). The olivine is partially enclosed in silicate glass (gray) and adhering plagioclase (white) crystals. This model&nbsp;shows the morphology of this olivine crystal that includes subgrains and melt channels (often referred to as embayments or re-entrants) that connect from the outside of the grain and extend into the grain&rsquo;s center.</p>