1 10 1 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/4963168143d5798d297e785330774a09.jpg db44deb968efb3a2ec86b6f143ebd868 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/87e0cb01dbb7b0b5d89066e0bdcaaf65.jpg c17b6506032fce0db90eece9ccce9f17 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/6059573330880ea41150025d6cfaf808.jpg 8dfef0d9df9d5721739f1e3d66aaeeee Physical Object An inanimate, three-dimensional object or substance. Note that digital representations of, or surrogates for, these objects should use Moving Image, Still Image, Text or one of the other types. Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource <h2><strong>L113<br /></strong></h2> <h2>Rhyolite, glassy (obsidian)</h2> Subject The topic of the resource <h3>Age</h3> <div class="element-text"> <p>Cenozoic</p> <h3>Location</h3> <div class="element-text"> <p>Yellowstone, U.S.A.</p> </div> </div> Description An account of the resource <div class="element"> <div class="element-text five columns omega"> <div class="element"> <div class="element-text five columns omega"> <p><em>NB, the term ‘obsidian’ refers to a jet-black glassy rock. It usually has a rhyolitic composition, but not always.</em></p> </div> </div> <div class="element"> <div class="element-text five columns omega"> <div class="element-set"> <div class="element"> <h3>Hand Specimen</h3> <div class="element-text"> <p>Black rock with the characteristic<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/265">vitreous lustre</a><span> </span>and<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/182">conchoidal fracture</a><span> </span>of<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/200">glass</a>.<span> </span><br />The surfaces are scattered with tiny spherical holes. These are<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/264">vesicles</a>.</p> </div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Holding the thin-section up to the light, the spherical<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/264">vesicles</a><span> </span>within the brown glass are clearly visible.</p> <p>Under the microscope the pale brown glass is scattered with tiny opaque speckles in a weak flow texture.</p> <p>Spherical vesicles are mostly filled in with mounting medium; notice its distinctive appearance under cross-polarised light. There are a small number of opaque infilled circles. These could be artefacts or black clumps of iron oxide.</p> <p>Tiny crystals are scattered throughout the glass, indicating that some devitrification has occurred. Circles of devitrification, probably nucleated on oxide crystals.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Glass → Very rapidly cooled magma. Probably<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/191">extrusive</a>.<span> </span><br />Vesicles: perfectly spherical, indicating that they were not being sheared by magma flow, i.e. the magma was not flowing.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text"> <p>glassy rhyolite<br />glass<br />obsidian</p> </div> </div> </div> </div> </div> </div> </div> felsic glassy vesicle