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    <pubDate>Tue, 09 Apr 2024 21:16:17 +0100</pubDate>
    <managingEditor>p1acollections@esc.cam.ac.uk (1A Collections)</managingEditor>
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    <item>
      <title><![CDATA[L110
Rhyolite, porphyritic (quartz porphyry)]]></title>
      <link>https://wserv3.esc.cam.ac.uk/p1acollections/items/show/5</link>
      <description><![CDATA[<div class="element-set">
            <div id="dublin-core-title" class="element">
        <h3>Title</h3>
                    <div class="element-text"><h2><strong>L110<br /></strong></h2>
<h2>Rhyolite, porphyritic (quartz porphyry)</h2></div>
            </div><!-- end element -->
        <div id="dublin-core-subject" class="element">
        <h3>Subject</h3>
                    <div class="element-text"><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></div>
            </div><!-- end element -->
        <div id="dublin-core-description" class="element">
        <h3>Description</h3>
                    <div class="element-text"><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></div>
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<div class="item-file image-jpeg"><a class="download-file" href="https://wserv3.esc.cam.ac.uk/p1acollections/files/original/d1bcada3b82f04f017d8a0e8b86f72b3.jpg"><img class="thumb" src="https://wserv3.esc.cam.ac.uk/p1acollections/files/square_thumbnails/d1bcada3b82f04f017d8a0e8b86f72b3.jpg" alt="L110_HS.jpg" title="L110_HS.jpg"></a></div><div class="item-file image-jpeg"><a class="download-file" href="https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f7281678c485abb0e71780e0b9119a47.jpg"><img class="thumb" src="https://wserv3.esc.cam.ac.uk/p1acollections/files/square_thumbnails/f7281678c485abb0e71780e0b9119a47.jpg" alt="L110_TS_ppl.jpg" title="L110_TS_ppl.jpg"></a></div><div class="item-file image-jpeg"><a class="download-file" href="https://wserv3.esc.cam.ac.uk/p1acollections/files/original/a7983a9ced24e5578ce7e9e61cac9c9c.jpg"><img class="thumb" src="https://wserv3.esc.cam.ac.uk/p1acollections/files/square_thumbnails/a7983a9ced24e5578ce7e9e61cac9c9c.jpg" alt="L110_TS_xpl.jpg" title="L110_TS_xpl.jpg"></a></div>]]></description>
      <pubDate>Thu, 13 Jun 2019 14:25:01 +0100</pubDate>
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    </item>
    <item>
      <title><![CDATA[L100
Alkali granite]]></title>
      <link>https://wserv3.esc.cam.ac.uk/p1acollections/items/show/1</link>
      <description><![CDATA[<div class="element-set">
            <div id="dublin-core-title" class="element">
        <h3>Title</h3>
                    <div class="element-text"><h2><strong>L100<br /></strong></h2>
<h2>Alkali granite</h2></div>
            </div><!-- end element -->
        <div id="dublin-core-subject" class="element">
        <h3>Subject</h3>
                    <div class="element-text"><h3>Specimen Age</h3>
<p>Variscan , Permo-Carboniferous</p>
<h3></h3></div>
            </div><!-- end element -->
        <div id="dublin-core-description" class="element">
        <h3>Description</h3>
                    <div class="element-text"><h3><span style="font-size:14px;">Hand Specimen</span></h3>
<div class="element-set">
<div class="element">
<div class="element-text">
<p>This rock has a<span> </span><a href="/p1acollections/items/show/244">porphyritic</a><span> </span>texture.<span> </span><a href="/p1acollections/items/show/236">Phenocrysts</a><span> </span>of white feldspar up to 30mm long are surrounded by a coarse<span> </span><a href="/p1acollections/items/show/205">groundmass</a><span> </span>of quartz, biotite and white feldspar.</p>
</div>
</div>
<div class="element">
<h3>Thin-section</h3>
<div class="element-text">
<p>Alkali feldspar (orthoclase)<span> </span><br />- Grains typically 2-4mm long,<span> </span><a href="/p1acollections/items/show/256">subhedral</a><span> </span>to<span> </span><a href="/p1acollections/items/show/173">anhedral</a>, dirty looking due to<span> </span><a href="/p1acollections/items/show/170">alteration</a>. Many display a<span> </span><a href="/p1acollections/items/show/228">microperthite texture</a>.</p>
<p>Plagioclase feldspar<span> </span><br />- Grains typically 1-4mm long, subhedral, characteristic<span> </span><a href="/p1acollections/items/show/169">lamellar twinning</a>. Many of the grains look “dirty” under plain polarised light, and have high<span> </span><a href="/p1acollections/items/show/177">birefringence</a><span> </span>speckles under cross-polarised light. They have been partially altered to white mica. Some grains are<span> </span><a href="/p1acollections/items/show/267">zoned</a>.</p>
<p>Quartz<span> </span><br />- Grains typically 1-4mm across, anhedral. They are characteristically clean and unaltered when compared with feldspar grains, but do contain many tiny<span> </span><a href="/p1acollections/items/show/210">inclusions</a>.</p>
<p>Biotite<span> </span><br />- Grains similar size as the rest of the<span> </span><a href="/p1acollections/items/show/205">groundmass</a>. Strongly<span> </span><a href="/p1acollections/items/show/239">pleochroic</a><span> </span>in pale straw and dark reddish brown. Speckled<span> </span><a href="/p1acollections/items/show/190">extinction</a>. Some sections show the one good<span> </span><a href="/p1acollections/items/show/180">cleavage</a><span> </span>of biotite. Small black blobs and circles are dotted all over the crystals. These are<span> </span><a href="/p1acollections/items/show/238">pleochroic haloes</a>, produced by zircons. Partially decomposed to chlorite.</p>
<p>Accessory minerals<span> </span><br />- Apatite<span> </span><br />- Small irregular grains of muscovite mica</p>
</div>
</div>
<div class="element">
<h3>Rock History</h3>
<div class="element-text">This is a coarse-grained rock, which must have cooled slowly as part of an intrusion. Its granitic composition (essential quartz and feldspar) indicates that it was produced in a continental setting.</div>
</div>
<div class="element">
<h3>Rock Name</h3>
<div class="element-text">alkali granite</div>
</div>
</div></div>
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<div class="item-file image-jpeg"><a class="download-file" href="https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f05e63c01d867dcb78bad17121fd1d31.jpg"><img class="thumb" src="https://wserv3.esc.cam.ac.uk/p1acollections/files/square_thumbnails/f05e63c01d867dcb78bad17121fd1d31.jpg" alt="L100.jpg" title="L100.jpg"></a></div><div class="item-file image-jpeg"><a class="download-file" href="https://wserv3.esc.cam.ac.uk/p1acollections/files/original/8a6e1a596d0d3bc7ae44e61aab691d56.jpg"><img class="thumb" src="https://wserv3.esc.cam.ac.uk/p1acollections/files/square_thumbnails/8a6e1a596d0d3bc7ae44e61aab691d56.jpg" alt="L100_thin_section.jpg" title="L100_thin_section.jpg"></a></div><div class="item-file image-jpeg"><a class="download-file" href="https://wserv3.esc.cam.ac.uk/p1acollections/files/original/4b619fdf5cbd3e05bf7ad22b3494cef3.jpg"><img class="thumb" src="https://wserv3.esc.cam.ac.uk/p1acollections/files/square_thumbnails/4b619fdf5cbd3e05bf7ad22b3494cef3.jpg" alt="L100_thin_section_xpl.jpg" title="L100_thin_section_xpl.jpg"></a></div>]]></description>
      <pubDate>Wed, 12 Jun 2019 12:05:16 +0100</pubDate>
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