1
10
264
-
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f05e63c01d867dcb78bad17121fd1d31.jpg
2d73462e69c78971d66f92dd5d6e622b
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/8a6e1a596d0d3bc7ae44e61aab691d56.jpg
84814d5a6509f76521cd808580d14224
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bdc304f5ffbdb6cb553489a47568c9ca
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>L100<br /></strong></h2>
<h2>Alkali granite</h2>
Subject
The topic of the resource
<h3>Specimen Age</h3>
<p>Variscan , Permo-Carboniferous</p>
<h3></h3>
Description
An account of the resource
<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>
coarse
continental
felsic
inclusions
-
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/744797d8340f3fb3bb5223f8d6e813df.jpg
2216573b7943b4d2108e89ba7c1ae3ee
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/6ca84b87271026626b96c159bfd42604.jpg
5fed78d37132afb7111530b3f05d4631
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/6e5325c5d9551839979a6bc06bdf7a19.jpg
d843ba39bcd4aa3e3a92b6b8306412a7
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>L101<br /></strong></h2>
<h2>Granite</h2>
Subject
The topic of the resource
<h3><strong>Age</strong></h3>
Caledonian, Devonian<br /><br /><h3><strong> Location</strong></h3>
Shap Fell, Cumbria
Description
An account of the resource
<div class="element-set">
<div class="element">
<div class="element-text">
<h3 class="element-set"><strong>Hand</strong> Specimen</h3>
<div class="element-set">
<div class="element">
<div class="element-text">
<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&query_type=keyword&record_types%5B%5D=Item&record_types%5B%5D=File&record_types%5B%5D=Collection&record_types%5B%5D=Exhibit&record_types%5B%5D=ExhibitPage&record_types%5B%5D=SimplePagesPage&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>
<div class="element">
<h3>Thin-section</h3>
<div class="element-text">
<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>
</div>
</div>
<div class="element">
<h3>Rock History</h3>
<div class="element-text">
<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>
</div>
</div>
<div class="element">
<h3>Advanced Notes</h3>
<div class="element-text">
<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>
</div>
</div>
<div class="element">
<h3>Rock Name</h3>
<div class="element-text">
<p>granite<br />adamellite</p>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
alkali
alteration
feldspar
-
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/e3160631658548f9f2dc6e1becea70da.jpg
d95ec5a176a934d2c3e57276e230693c
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/e2173d02d96267ba32160e6fdf7413e7.jpg
6064d39c4c259244a0f9ee941313b06b
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/01845924716bedfe0fd182d669f227cd.jpg
29966d5660a6a3fe8f268bf574236f17
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/16d925108b74372b95b4fdde50676900.jpg
5258ac41a282f9310c3fe1c4115cc800
https://wserv3.esc.cam.ac.uk/p1acollections/files/original/f8b28219498294d826754ab3542fb00f.jpg
c99a49a3bc0d2fc2234806df01cd66c1
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27acfdf84cb9a638c01a6ee7daebba0e
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>L102<br /></strong></h2>
<h2>Hornblende biotite granite</h2>
Subject
The topic of the resource
<h3>Age</h3>
<div class="element-text">
<p>Caledonian, Devonian</p>
<h3>Location</h3>
<div class="element-text">
<p>Glencoe</p>
</div>
</div>
Description
An account of the resource
<div class="element-set">
<div class="element">
<div class="element-text">
<div class="element-set">
<div class="element">
<div class="element-text">
<h3><span style="font-size:14px;">Hand Specimen</span></h3>
</div>
</div>
</div>
<div class="element-set">
<div class="element">
<div class="element-text">
<p>Medium to coarse-grained rock with a<span> </span><a href="/p1acollections/items/show/203">granular</a><span> </span>texture.<span> </span><br />White feldspar<span> </span><a href="/p1acollections/items/show/215">laths</a><span> </span>2-4 mm long are clearly visible.<span> </span><br />Other phases: pink feldspar, black biotite mica, black hornblende amphibole and pale grey quartz. These grains are more<span> </span><a href="/p1acollections/items/show/188">equant</a>, typically 1-2 mm across.<span> </span><br />Biotite may be distinguished from hornblende by its flaky<span> </span><a href="/p1acollections/items/show/206">habit</a><span> </span>and one good<span> </span><a href="/p1acollections/items/show/180">cleavage</a>. It is shinier than hornblende.</p>
</div>
</div>
<div class="element">
<h3>Thin-section</h3>
<div class="element-text">
<p>Plagioclase feldspar<span> </span><br />- The larger laths (2-4 mm long) are strongly<span> </span><a href="/p1acollections/items/show/267">zoned</a>. The cores of these laths, which display clear<span> </span><a href="/p1acollections/items/show/169">lamellar twinning</a>, have been<span> </span><a href="/p1acollections/items/show/232">overgrown</a><span> </span>by rims of more feldspar. Some<span> </span><a href="/p1acollections/items/show/170">alteration</a><span> </span>to white mica.</p>
<p>Biotite mica<span> </span><br />- Grains typically 1 mm across. Strongly pleochroic in reddish brown and pale straw. Often associated with small grains of an opaque accessory mineral, probably magnetite.</p>
Quartz<span> </span><br />- Grains are 1-2 mm across,<span> </span><a href="/p1acollections/items/show/173">anhedral</a>, and display<span> </span><a href="/p1acollections/items/show/263">undulose extinction</a>.
<p>Alkali feldspar<span> </span><br />- Anhedral grains up to 5mm long. Some alteration to white mica. Some grains display a<span> </span><a href="/p1acollections/items/show/228">microperthite texture</a>.</p>
<p>Hornblende amphibole<span> </span><br />- Pale green, anhedral. Grains appear to have been “eaten away”, reducing their<span> </span><a href="/p1acollections/items/show/246">prismatic</a><span> </span>form (diamond) to a ragged anhedral<span> </span><a href="/p1acollections/items/show/206">form</a>. Amphiboles have two cleavage planes which intersect at 56°.</p>
</div>
</div>
<div class="element">
<h3>Rock History</h3>
<div class="element-text">This coarse-grained rock must have cooled slowly as part of an intrusion.<br /><br />Its granitic composition (essential quartz and feldspar) indicates that it was produced in a continental setting.<br /><br />Strongly zoned plagioclase crystals and “eaten away” appearance of the hornblende could be due to a change in the composition of the liquid from which the phases crystallised; perhaps due to magma mixing or degassing of volatiles from the magma.<span> </span><br /><br />Presence of hornblende and biotite indicate that this is a wet granite, probably from a subduction zone.<br /><br />Hydrothermal alteration of feldspars to white mica.</div>
</div>
<div class="element">
<h3>Advanced Notes</h3>
<div class="element-text">
<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, with additional quartz and biotite.</p>
</div>
</div>
<div class="element">
<h3>Rock Name</h3>
<div class="element-text">
<p>hornblende biotite granite<br />adamellite</p>
</div>
</div>
</div>
</div>
</div>
</div>
arc
biotite
coarse
granite
hornblende
subduction
-
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
-
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/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">
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<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>
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<div class="element-text five columns omega">
<div class="element-set">
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<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
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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>
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<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
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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">
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<div class="element-text five columns omega">
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<div class="element-text"></div>
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<div class="element-text">
<h3>Hand Specimen</h3>
</div>
</div>
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<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 <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
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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/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">
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</div>
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<div class="element">
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<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