1 10 2 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/8c4e9f36beb5bdf91c3074408b01ccb0.jpg 8d6162debca1ae51b62f6d3fa743c662 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f5b37535e34701668500f4bbe72bc177.jpg 89547f12b6956f7a89eb9343ae4b2e08 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/7e2698eb1f83d2a13be41526939fc1c4.jpg 92e7719401b0ee848bad92f1f3c3f023 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>L141<br /></strong></h2> <h2>Gabbro</h2> Description An account of the resource <div class="element"> <div class="element"> <div class="element-text five columns omega"> <div class="element"> <h3>Hand Specimen</h3> <div class="element-text">Very dark grey, coarse-grained rock, typical grain size 1-2 mm.<span> </span><br />Main mineral phases are black clinopyroxene, greenish olivine and pale grey feldspar. The rock is cross-cut by a small number of hairline white veins.</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/258">Tabular</a><span> </span>phenocrysts making-up ~50% of the rock. Characteristic<span> </span><a href="/p1acollections/items/show/169">lamellar twinning</a>. Some are<span> </span><a href="/p1acollections/items/show/267">zoned</a>.</p> <p>Olivine<span> </span><br />-<span> </span><a href="/p1acollections/items/show/236">Phenocrysts</a><span> </span>have been extensively altered, rendering them almost unrecognisable. The olivine has decomposed to magnetite and serpentine. Relict olivine grains display characteristic curving cracks and<span> </span><a href="/p1acollections/items/show/189">euhedral</a><span> </span><a href="/p1acollections/items/show/206">form</a>.</p> <p>Clinopyroxene (augite)<span> </span><br />-<span> </span><a href="/p1acollections/items/show/211">Interstitial</a><span> </span>grains making-up ~35% of the rock.<span> </span><a href="/p1acollections/items/show/241">Poikilitic</a><span> </span>texture. Inclined<span> </span><a href="/p1acollections/items/show/190">extinction</a>. Interference colours from first order pink to second order orange. Pale grey under plane polarised light. Some simple twinning.</p> <p>Accessory minerals<span> </span><br />- Opaque, interstitial, probably magnetite.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Coarse grained → slowly cooled,<span> </span><a href="/p1acollections/items/show/212">intrusive</a>.<span> </span><br />Hydrothermal<span> </span><a href="/p1acollections/items/show/170">alteration</a><span> </span>of olivine after crystallisation of the rock.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">gabbro</div> </div> </div> </div> </div> alteration interstitial intrusive mafic phenocryst 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