1 10 2 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/7b7f1ba53fca171d08e85f7165d1330d.jpg 3f0131a7e6802310254284a8c2b5dedb https://wserv3.esc.cam.ac.uk/p1acollections/files/original/a80c30b1e44c57fd7e5cd8ccb0e22649.jpg 324282e4d846cb1d25996476c51bf0ac https://wserv3.esc.cam.ac.uk/p1acollections/files/original/d0b428c197fabf498b5cc2789834ede6.jpg c32bf03df5c51ff80285c039ec70939e 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>L130<br /></strong></h2> <h2>Andesite, porphyritic (porphyrite)</h2> Subject The topic of the resource <h3>Age</h3> <div class="element-text"> <p>Early Paleozoic</p> <h3>Location</h3> <div class="element-text"> <p>Cansip Porphyry Sills<br />Sutherland</p> </div> </div> Description An account of the resource <div class="element-set"> <div class="element"> <div class="element-text"> <div class="element"> <div class="element-text five columns omega"> <div class="element"> <div class="element-text five columns omega"> <div class="element-text"> <div class="element-text"></div> </div> </div> </div> <div class="element"> <div class="element-text five columns omega"> <div class="element-set"> <div class="element"> <div class="element-text"> <h3>Hand Specimen</h3> </div> </div> </div> <div class="element-set"> <div class="element"> <div class="element-text"> <p><a href="/p1acollections/items/show/244">Porphyritic</a>.<span> </span><br />Large,<span> </span><a href="/p1acollections/items/show/258">tabular</a>, pale grey-yellow<span> </span><a href="/p1acollections/items/show/236">phenocrysts</a><span> </span>of plagioclase feldspar, randomly oriented, twin striations are visible on many of them.<span> </span><br />Pink-brown<span> </span><a href="/p1acollections/items/show/184">cryptocrystalline</a><span> </span>groundmass contains black, shiny flakes of biotite.</p> </div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Plagioclase feldspar<span> </span><br />-<span> </span><a href="/p1acollections/items/show/189">Euhedral</a><span> </span>phenocrysts, 2-20 mm long, displaying the characteristic<span> </span><a href="/p1acollections/items/show/169">lamellar twinning</a>. Some<span> </span><a href="/p1acollections/items/show/170">alteration</a><span> </span>to white mica. In places they have been replaced by chlorite and calcite.</p> <p>Biotite<span> </span><br />- Phenocrysts, most &lt;1mm long, with characteristic brown to pale straw pleochroism and straight<span> </span><a href="/p1acollections/items/show/190">extinction</a>.</p> <p>Accessory minerals<span> </span><br />- Quartz<span> </span><br />- Apatite</p> <p>Groundmass<span> </span><br />- Mainly cryptocrystalline. A small number of feldspar grains can be identified. Small ragged<span> </span><a href="/p1acollections/items/show/264">vesicles</a>.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Two-stage cooling: phenocrysts followed by<span> </span><a href="/p1acollections/items/show/205">groundmass</a>.<span> </span><br />Phenocrysts are euhedral indicating that they crystallised free-floating in a magma chamber.<span> </span><br />The fine-grained groundmass must have crystallised rapidly due to cooling at the Earth’s surface.<span> </span><br />Alteration occurred after crystallisation.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">porphyritic andesite<br />porphyrite</div> </div> </div> </div> </div> </div> </div> </div> </div> </div> alteration groundmass phenocryst porphyritic https://wserv3.esc.cam.ac.uk/p1acollections/files/original/d1bcada3b82f04f017d8a0e8b86f72b3.jpg 132f0e00763d982d7b38233c335bea76 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f7281678c485abb0e71780e0b9119a47.jpg cbe05af402dff631ae66cc0a04916568 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/a7983a9ced24e5578ce7e9e61cac9c9c.jpg d1374b7286c25297bfe7fa333bd490d0 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>L110<br /></strong></h2> <h2>Rhyolite, porphyritic (quartz porphyry)</h2> Subject The topic of the resource <h3>Age</h3> <div class="element-text"> <p>Ordovician</p> <h3>Location</h3> <div class="element-text"> <p>Armboth Dyke <br />Thirlmere, Cumbria</p> </div> </div> Description An account of the resource <div class="element"> <h3>Hand Specimen</h3> <div class="element-text"> <p>Pink-brown,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/244">porphyritic</a><span> </span>rock with a very fine-grained<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/205">groundmass</a>.<span> </span><br />Abundant pink<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/221">macrocrysts</a><span> </span>(5-10 mm).<span> </span><br /><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/236">Phenocrysts</a><span> </span>of feldspar (2-4 mm) and quartz (2-4 mm).<span> </span><br />Accessory black mineral.</p> </div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Quartz<span> </span><br />- Rounded phenocrysts (1-4 mm) with embayments/cavities and tiny<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/210">inclusions</a>.</p> <p>Feldspar<span> </span><br />- Phenocrysts ~2mm,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/256">subhedral</a>. Mainly alkali feldspar, some plagioclase.<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/170">Alteration</a> to white mica.</p> <p>Garnet<span> </span><br />- Very rare,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/189">euhedral</a><span> </span>phenocrysts (0.5-1 mm).<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/213">Isotropic</a>, high<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/247">relief</a>, colourless to pale pink.</p> <p>Biotite<span> </span><br />- Very rare fragments with chlorite alteration.</p> <p>Groundmass<span> </span><br />-<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/227">Microcrystalline</a><span> </span>quartz and feldspar, with some muscovite and biotite.</p> <p>Calcite<span> </span><br />- Some of the feldspars phenocrysts and most of the garnet phenocrysts have been replaced by calcite. These are the pink macrocrysts visible in hand specimen.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text">Porphyritic texture indicates two-stage cooling. The phenocrysts grew slowly in a magma chamber; the fine-grained groundmass formed during rapid cooling at the Earth’s surface.<br /><br />Late stage hydrothermal alteration to white mica and carbonate.</div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">porphyritic rhyolite<br />quartz porphyry</div> </div> alteration inclusions porphyritic