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    <pubDate>Tue, 09 Apr 2024 21:16:13 +0100</pubDate>
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      <title><![CDATA[L101
Granite]]></title>
      <link>https://wserv3.esc.cam.ac.uk/p1acollections/items/show/2</link>
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        <h3>Title</h3>
                    <div class="element-text"><h2><strong>L101<br /></strong></h2>
<h2>Granite</h2></div>
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        <h3>Subject</h3>
                    <div class="element-text"><h3><strong>Age</strong></h3>
Caledonian, Devonian<br /><br /><h3><strong> Location</strong></h3>
Shap Fell, Cumbria</div>
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        <h3>Description</h3>
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<h3 class="element-set"><strong>Hand</strong> Specimen</h3>
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<p>Coarse-grained,<span> </span><a href="/p1acollections/items/show/244">porphyritic</a><span> </span>texture.<span> </span><br /><a href="/p1acollections/items/show/236">Phenocrysts</a><span> </span>of pink feldspar, 10-30 mm long,<span> </span><a href="/p1acollections/items/show/258">tabular</a>, display clear<span> </span><a href="/p1acollections/items/show/180">cleavage</a> planes.<span> </span><br /><a href="/p1acollections/search?query=groundmass&amp;query_type=keyword&amp;record_types%5B%5D=Item&amp;record_types%5B%5D=File&amp;record_types%5B%5D=Collection&amp;record_types%5B%5D=Exhibit&amp;record_types%5B%5D=ExhibitPage&amp;record_types%5B%5D=SimplePagesPage&amp;submit_search=Search">Groundmass</a><span> </span>of coarse-grained white feldspar, pink feldspar, quartz and biotite.<span> </span><br />Quartz grains are<span> </span><a href="/p1acollections/items/show/173">anhedral</a><span> </span>and display their characteristic<span> </span><a href="/p1acollections/items/show/182">conchoidal fracture</a><span> </span>and<span> </span><a href="/p1acollections/items/show/265">vitreous lustre</a>.</p>
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<h3>Thin-section</h3>
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<p>Alkali feldspar (orthoclase)<span> </span><br />- Pink phenocrysts up to ~10 mm long, relatively fresh (unaltered).</p>
<p>Groundmass<span> </span><br />- Feldspar (both plagioclase and alkali) grains 1-4mm long, mainly<span> </span><a href="/p1acollections/items/show/256">subhedral</a>, though some are quite<span> </span><a href="/p1acollections/items/show/215">lath</a><span> </span>shaped. Partially altered. The plagioclase grains display their characteristic<span> </span><a href="/p1acollections/items/show/169">lamellar twinning</a>.<span> </span><br />- Biotite grains (0.5-2 mm) with subhedral to anhedral<span> </span><a href="/p1acollections/items/show/206">form</a>. Grains have ragged edges and are partially altered to chlorite, mainly along<span> </span><a href="/p1acollections/items/show/180">cleavage</a><span> </span>planes.<span> </span><br />- Quartz grains (typically 2-5 mm) contain lots of tiny<span> </span><a href="/p1acollections/items/show/210">inclusions</a><span> </span>and display<span> </span><a href="/p1acollections/items/show/263">undulose extinction</a>.</p>
<p>Accessory minerals<span> </span><br />- Sphene<span> </span><br />- Apatite<span> </span><br />- Opaque mineral</p>
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<h3>Rock History</h3>
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<p>Porphyritic texture means this rock underwent two stages of cooling; phenocrysts crystallised first followed by the groundmass. The groundmass is coarse-grained, and must have crystallised slowly as part of an intrusion.</p>
<p>Plagioclase and alkali feldspar both occur in this rock, indicating that it formed at high pressures.</p>
<p>Granitic composition (essential quartz and feldspar) indicates that it was produced in a continental setting. Late-stage<span> </span><a href="/p1acollections/items/show/170">alteration</a>.</p>
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<h3>Advanced Notes</h3>
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<p>This rock is classified as an<span> </span><span>adamellite</span><span> </span>because it contains roughly equal proportions of alkali feldspar and plagioclase feldspar, as well as biotite and quartz.</p>
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<h3>Rock Name</h3>
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<p>granite<br />adamellite</p>
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      <pubDate>Wed, 12 Jun 2019 12:09:47 +0100</pubDate>
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