26 10 264 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/84c1834164497c8491f5db12efcef6d2.jpg c9a7faba04f5ca2d06682176ab35e8a8 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/b718221d8d279140605b8befd4e9d749.jpg 691b6ce9581e994fa11d953b4fd41bfb https://wserv3.esc.cam.ac.uk/p1acollections/files/original/c501e1086a63d3623e85cb1f1be70780.jpg b09c139b55148cacb06439964118c472 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>L200<br /></strong></h2> <h2>Volcanic Breccia</h2> Subject The topic of the resource <h3>Age</h3> <div class="element-text"> <p>Carboniferous</p> <h3>Location</h3> <div class="element-text"> <p>Melrose, Scotland</p> </div> </div> Description An account of the resource <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>Sedimentary textures, very poorly sorted.<span> </span><br />Sub-round to angular grains up to 20mm across.<span> </span><br />Wide variety of clasts: dark purple, cream, rusty orange, grey, several types of lava.<span> </span><br />Some black, shiny igneous crystals.<span> </span><br />Brown-grey matrix of<span> </span><a href="/p1acollections/items/show/266">volcanic</a><span> </span>ash.</p> </div> </div> <div class="element"> <h3>Thin section</h3> <div class="element-text">Wide range of clasts including<br />- Basalt<br />- Slate or phyllite<br />- Schist<br />- Chert<br />- Sandstone<br />- Carbonate<br />- Quartz<br /><br />Matrix of fine volcanic ash.</div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text">This is an example of the coarser type of material deposited by explosive volcanic action.<br /><br />NB,<br />This is not a typical volcanic breccia, as one usually sees a greater abundance of igneous clasts; other clasts could be wall-rock. Another name for this rock could be “lithic wacke”.</div> </div> <div class="element"></div> <div class="element"></div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">volcanic breccia<br />lithic wacke</div> </div> </div> clastic extrusive lithic https://wserv3.esc.cam.ac.uk/p1acollections/files/original/3a045ee9b56d4f42ca318e0623d82bac.jpg 9de28fb8f3aa176785607b86ed35a349 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/ad163c9708faad229d3b45dfe05cc6d2.jpg c1d47de48160ed5d95eaa51938891095 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/9a8a6274518a04739a23711773ab19ae.jpg 9d09b58110825fcd56646bf1cec98d2b 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>L172<br /></strong></h2> <h2>Ultramafic cumulate</h2> Subject The topic of the resource <h3>Age</h3> <div class="element-text">Precambrian<br /><br /><h3>Location</h3> <div class="element-text">Lewisian Complex, Dyke<br />Assynt, Sutherland</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"> <h3>Hand Specimen</h3> </div> </div> <div class="element"> <div class="element-text five columns omega"> <div class="element-set"> <div class="element"> <div class="element-text">Greenish black, coarse-grained rock, comprising olivine, clinopyroxene and plagioclase.<br />Grains typically 1-2 mm across.<span> </span></div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Olivine<span> </span><br />-<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/256">Subhedral</a><span> </span>to<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/189">euhedral</a><span> </span>grains making up ~45% of the rock.<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/170">Alteration</a><span> </span>to magnetite and serpentine, particularly along the curving cracks. Cracks across the thin-section, could be due to expansion of the rock as the olivine was altered.</p> <p>Clinopyroxene<span> </span><br />-<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/211">Interstitial</a><span> </span>phase making up ~35% of the rock. Moderate<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/247">relief</a>, inclined<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/190">extinction</a> and first order pink to second order orange interference colours.</p> <p>Plagioclase feldspar<span> </span><br />- Interstitial phase making up ~20% of the rock. Low first order interference colours and<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/169">lamellar twinning</a>.</p> <p>Accessory minerals - Biotite, small, interstitial grains, altered.</p> <p>This is a cumulate rock. It has undergone late-stage shear banding.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Olivine<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/236">phenocrysts</a><span> </span>crystallised first.<span> </span><br />Clinopyroxene grew around the olivine phenocrysts.<span> </span><br />Interstitial feldspar filled in the remaining gaps.<span> </span><br />Shearing of the rock produced bands of deformation.<span> </span><br />Hydrothermal alteration.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">ultramafic cumulate</div> </div> </div> </div> </div> </div> </div> </div> alteration euhedral interstitial shear ultramafic https://wserv3.esc.cam.ac.uk/p1acollections/files/original/852a77355d6e4e7f6cf8052de0bf7a9d.jpg 3418fba1e4453736b6dbd51d55fd9583 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/aab79550a27397bff8be8a5cb67ef43f.jpg f5f51d065ee3cc8e993e930077cbd5fc https://wserv3.esc.cam.ac.uk/p1acollections/files/original/1c200ce8cf23f154e881c3c62ad865c8.jpg 25a8c42f179836492f49a6fdb0bcbb5f https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f3204ba875eb0b5fb7aaffafd6e91261.jpg 6a3a28ccf49c7653bc57780b5eacdd11 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/57c910796611238dbf565e32ca5fc702.jpg d53f7084c610e651bdaf2389f9297e28 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>L162<br /></strong></h2> <h2>Basalt, porphyritic</h2> Subject The topic of the resource <h3>Specimen Age</h3> <div class="element-text"> <p>Carboniferous</p> <h3>Location</h3> <div class="element-text"> <p>Volcanic neck, Lion's Haunch, Arthur's Seat, Edinburgh</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-text"> <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> </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>Black,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/244">porphyritic</a><span> </span>rock comprising black clinopyroxene, grey feldspar and greenish olivine<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/236">phenocrysts</a>, in a fine-grained<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/205">groundmass</a>.</p> </div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Plagioclase feldspar<span> </span><br />- Phenocrysts 1-4mm long, with a euhedral,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/258">tabular</a><span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/206">form</a>. Randomly orientated. Characteristic<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/169">lamellar twinning</a>. Some are<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/267">zoned</a>.<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/210">Inclusions</a><span> </span>of magnetite, clinopyroxene and other minerals. Extensive<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/170">alteration</a><span> </span>along abundant cracks.</p> <p>Clinopyroxene (augite)<span> </span><br />-<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/189">Euhedral</a><span> </span>phenocrysts, 1-2 mm across. Moderate<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/247">relief</a>, inclined<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/190">extinction</a><span> </span>and first order pink to second order orange interference colours. Pale pink in thin-section. Some are<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/267">zoned</a>.</p> <p>Olivine<span> </span><br />- Very few phenocrysts are fresh enough to be easily identifiable. These are colourless in plane polarised light, have moderate relief, and up to second order pink interference colours. No<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/180">cleavage</a>.</p> <p>- 1st phase of alteration along cracks: The majority of the phenocrysts have been completely altered to greenish serpentine.</p> <p>- 2nd phase of alteration: orange brown mineral – probably the amphibole<span> </span><span>cummingtonite</span>. Characteristic curving cracks and the<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/246">prismatic</a><span> </span>form of olivine are still visible.</p> <p>Groundmass<span> </span><br />- Fine-grained. Plagioclase feldspar needles, clinopyroxene, some olivine (mostly altered), and opaques, probably magnetite. Occasional calcite grain.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Two stage cooling<span> </span><br />1. Phenocrysts grow slowly in a magma chamber.<span> </span><br />2. Fine-grained groundmass grew rapidly →<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/191">extrusive</a>.<span> </span><br />Hydrothermal alteration, possibly as part of the<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/266">volcanic</a><span> </span>pile.</p> </div> </div> <div class="element"> <h3>Advanced Notes</h3> <div class="element-text"><span>Cummingtonite</span><span> </span>is an amphibole. It is colourless to pale green in thin-section, has moderate relief and two cleavages which intersect at 56°.</div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">porphyritic basalt</div> </div> </div> </div> </div> </div> </div> </div> </div> </div> </div> </div> </div> </div> alteration extrusive volcanic https://wserv3.esc.cam.ac.uk/p1acollections/files/original/6ee5b4daa895a80c4f5d1219f546fd1f.jpg ec992c8fa5fc180cef9aa183c5fccb0b https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f04b282ccc316fc1d49d4170730b5892.jpg 7759e3afb21758ccf4ccadb89eb40ce9 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/d5a2b07e623f5f5b39a9506ee7ac050f.jpg 41972d8ec488fd6c039ae81709eaf2e3 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>L161<br /></strong></h2> <h2>Basalt, amygdaloidal</h2> Subject The topic of the resource <h3>Specimen Age</h3> <div class="element-text"> <p>Cenozoic</p> <h3>Location</h3> <div class="element-text"> <p>Lava, Skye</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-text"> <div class="element-text"> <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>Fine-grained, greenish black rock comprising dark and white minerals.<span> </span><br />Contains<span> </span><a href="/p1acollections/items/show/172">amygdales</a>, mostly white, though some have black cores.</p> </div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Fine-grained plagioclase<span> </span><a href="/p1acollections/items/show/215">laths</a><span> </span>and irregular clinopyroxene (augite) grains, replaced with calcite. Many of the plagioclase laths have been almost entirely altered.</p> <p>The amygdales are filled with<span> </span><span>zeolite</span>, growing in spherulitic and radiate patterns. Many have rims of calcite and fine-grained chlorite.</p> <p>Some vein material -<span> </span><a href="/p1acollections/items/show/203">granular</a><span> </span>quartz with<span> </span><a href="/p1acollections/items/show/257">sutured contacts</a>.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Fine-grained → rapid,<span> </span><a href="/p1acollections/items/show/191">extrusive</a><span> </span>crystallisation.<span> </span><br />Gas bubbles trapped within lava produced<span> </span><a href="/p1acollections/items/show/264">vesicles</a>.<span> </span><br />Circulation of fluids → precipitation of zeolite within the vesicles.</p> </div> </div> <div class="element"> <h3>Advanced Notes</h3> <div class="element-text"> <p><span>Zeolites</span><span> </span>are produced at low temperatures. They are commonly precipitated in basaltic volcanic piles.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">amygdaloidal basalt</div> </div> </div> </div> </div> </div> </div> </div> </div> </div> </div> </div> alteration extrusive mafic 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 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/c79ea7e24906cdc87124323d1c61c679.jpg 2dcf14e8ccd71331a82d77c757769562 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/65cc722b8ca1c5c78563e7830e432ad5.jpg 41095f6476cbd7f3f5fe86f7138c984c https://wserv3.esc.cam.ac.uk/p1acollections/files/original/560ec59ba2f299a27cb59a2103c356ac.jpg ac56cab3922729a7a2da4bfb245672a8 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>L120<br /></strong></h2> <h2>Granodiorite</h2> Subject The topic of the resource <h3>Age</h3> <div class="element-text">Caledonian, Devonian<br /><br /><h3>Location</h3> <div class="element-text">Boulder, Moor of Rannoch</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"> <h3>Hand Specimen</h3> </div> </div> <div class="element"> <div class="element-text five columns omega"> <div class="element-set"> <div class="element"> <div class="element-text">Mostly moderately coarse-grained (typically 1-2 mm), some regions finer-grained (typically ~0.5 mm).<span> </span><br />“Salt and pepper” appearance being speckled black and white. Two black phases, biotite mica and hornblende amphibole. White regions comprise quartz and white feldspar.</div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Hornblende amphibole<span> </span><br />- Pleochroic in greens and cream. Some of the grains display<span> </span><a href="/p1acollections/items/show/252">simple twinning</a>. Two<span> </span><a href="/p1acollections/items/show/180">cleavages</a><span> </span>intersect at 56°.</p> <p>Biotite<span> </span><br />-<span> </span><a href="/p1acollections/items/show/256">Subhedral</a><span> </span>to<span> </span><a href="/p1acollections/items/show/173">anhedral</a><span> </span>grains, pleochroic in brown and straw. Straight, speckled<span> </span><a href="/p1acollections/items/show/190">extinction</a>. Chlorite partially replaces biotite – late stage<span> </span><a href="/p1acollections/items/show/170">alteration</a>.</p> <p>Quartz<span> </span><br />- Anhedral,<span> </span><a href="/p1acollections/items/show/211">interstitial</a><span> </span>grains. They display<span> </span><a href="/p1acollections/items/show/263">undulose extinction</a><span> </span>and contain abundant tiny<span> </span><a href="/p1acollections/items/show/210">inclusions</a>, but are characteristically fresh and unaltered.</p> <p>Feldspar, mainly plagioclase<span> </span><br />- Mostly anhedral grains, though some are<span> </span><a href="/p1acollections/items/show/215">lath</a>-shaped. Alteration. Zonation.</p> <p>Accessory minerals:<span> </span><br />- Sphene<span> </span><br />- Magnetite<span> </span><br />- Apatite</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Rock history Hornblende is<span> </span><a href="/p1acollections/items/show/189">euhedral</a>. It is, therefore a primary igneous phase, and must have crystallised from a wet melt.</p> <p>Magma cooled relatively slowly, allowing large crystals to grow.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text">granodiorite</div> </div> </div> </div> </div> </div> </div> </div> coarse felsic interstitial 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 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/19912665ea9a172bdcbf89f42f8bfd51.jpg 02578476b62cb5d6f8f83c4fd82c21b1 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/fd32bc8c9301390886cfc2d1b5039e5b.jpg d750b6043096fff00dfac9d769fd8306 https://wserv3.esc.cam.ac.uk/p1acollections/files/original/e296e547f6d79fa4ce77b4b16eaafdb2.jpg 6c3117dea0a91029411225c36498d477 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>L112<br /></strong></h2> <h2>Rhyolite, banded</h2> Subject The topic of the resource <div class="element-text"> <h3>Location</h3> <div class="element-text"> <p>Glacial boulder, North Wales</p> </div> </div> Description An account of the resource <div class="element"> <h3>Hand Specimen</h3> <div class="element-text"> <p>Pink-brown, fine-grained rock.<span> </span><br />Strong planar shear<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/192">fabric</a>, produced by flow: streaks of dark red-brown and black-brown in the<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/205">groundmass</a>, and siliceous streaks and lenses.<span> </span><br />Gold-coloured,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/224">metallic</a><span> </span>pyrite, and a black mineral are associated with the quartz-filled lenses.</p> </div> </div> <div class="element"> <h3>Thin-section</h3> <div class="element-text"> <p>Plagioclase feldspar<span> </span><br />-<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/236">Phenocrysts</a>, fairly fresh,<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/258">tabular</a>, typically 1-2 mm long, with characteristic<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/169">lamellar twinning</a>.</p> <p>Opaques<span> </span><br />- Grains associated with the quartz-filled lenses. Range of sizes from<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/205">groundmass</a><span> </span>up to ~0.5 mm. These are a mixture of pyrite, FeS2, (tending to have a cubic<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/206">form</a>) and the unidentified black mineral, both seen in hand specimen.</p> <p>Groundmass<span> </span><br />-<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/184">Cryptocrystalline</a>, almost glassy, speckled with tiny, irregular quartz and feldspar crystals. Probably devitrified<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/200">glass</a>. Plagioclase altered to white mica.</p> <p>Secondary quartz<span> </span><br />- Narrow veins and lenses of quartz, considerably coarser than the groundmass. The grains of quartz have<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/257">sutured contacts</a>, and may have been injected after consolidation of the lava. Some of these clumps are rimmed with inward pointing needles of feldspar.</p> </div> </div> <div class="element"> <h3>Rock History</h3> <div class="element-text"> <p>Phenocrysts crystallised in a magma chamber. The magma erupted and cooled very rapidly to a fine-grained, glassy groundmass, preserving<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/197">flow banding</a><span> </span>texture. Injection of quartz-rich fluid, which precipitated quartz in lenses and veins.</p> <p>Very high temperature hydrothermal<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/170">alteration</a><span> </span>caused devitrification of the glassy groundmass.</p> </div> </div> <div class="element"> <h3>Rock Name</h3> <div class="element-text"> <p>banded rhyolite<br />rhyloite flow</p> </div> </div> devitrification flow shear 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