18 10 264 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Argillaceous</h2> Subject The topic of the resource <p>Rocks comprising, or containing a significant proportion of, clay are described as argillaceous.</p> Description An account of the resource <div> <div class="element-set"> <div class="element"> <div class="element-text"> <p><em>Have a look at the<strong> argillaceous limestone (<a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/29">L350</a>)</strong> in the 1A Reference Series.</em></p> </div> </div> </div> </div> <div> <div class="element"> <div class="element-text"></div> <div class="collection"></div> </div> </div> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Birefringence</h2> Subject The topic of the resource <p>Light passing through a mineral is resolved into two permitted vibration directions. In an anisotropic mineral light travels at different velocities along the two vibration directions. The ray travelling in the slow vibration direction will be retarded compared with the ray travelling in the fast vibration direction. On leaving the mineral grain the two rays will interfere, producing interference colours.</p> <p>When the slow ray exits the mineral grain the fast ray will already have exited the grain and travelled an additional distance know as the optical path difference, or retardation (Δ). This distance is proportional to the thickness of the mineral grain (t) and the difference in the refractive indices of the two vibration directions (n₁-n₂):</p> <p>Δ = t(n₁-n₂)</p> <p>The birefringence is the difference in the refractive indices of the two vibration directions (n₁-n₂).</p> <p>When rotated under cross-polarised light anisotropic minerals display changing interference colours called birefringencecolours. The birefringence (n₁-n₂) of the mineral can be determined from these colours using a Michel-Levy chart.</p> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Bladed</h2> <div class="element-set"> <div class="element"></div> <div class="element"></div> <div class="element"> <div class="element-text"></div> </div> </div> Subject The topic of the resource <span>Crystals with a flattened, elongate habit, resembling blades of grass are described as bladed. Bladed crystals are more elongate than platy crystals, and thinner than tabular crystals.</span> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Carlsbad twinning</h2> Subject The topic of the resource <div> <div class="element-set"> <div class="element"> <div class="element-text"> <p></p> </div> </div> </div> </div> <div> <div class="element"> <div class="element-text"></div> <div class="collection"></div> </div> </div> Description An account of the resource <em>See<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/252">simple twins</a>.</em> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Cleavage</h2> Subject The topic of the resource <div> <div class="element-set"> <div class="element"> <div class="element-text"> <p class="NoSpacing">Many minerals display very fine, parallel, straight lines called cleavage. Cleavages are the manifestation of planes of weakness within the crystal structure of the mineral. A single crystal may display cleavage in more than one orientation. For example, amphiboles have cleavages which intersect at ~56°, whereas pyroxenes have cleavages which intersect at 90°. </p> </div> </div> </div> </div> <div> <div class="element"> <div class="element-text"></div> <div class="collection"></div> </div> </div> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Colour index</h2> Subject The topic of the resource <div> <div class="element-set"> <div class="element"> <div class="element-text"> <p>Rocks can be classified according to their colour index (CI). This describes the proportion of ferromagnesian minerals, such as olivine, pyroxenes, amphiboles and biotite mica, they contain. Colour index is measured in volume percent. The terms used to describe the varying proportions of ferromagnesian minerals are:</p> <ul><li><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/209">hypermelanic</a>: &gt;90 vol% dark (mafic) minerals</li> <li><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/222">melanocratic</a>: &gt;60 vol% dark (mafic) minerals</li> <li><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/223">mesocratic</a>: 30-60 vol% dark (mafic) minerals</li> <li><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/218">leucocratic</a>: &lt;30 vol% dark (mafic) minerals</li> </ul></div> </div> </div> </div> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Conchoidal fracture</h2> Subject The topic of the resource <span>When a brittle material lacking cleavage (plane of weakness) fractures, it breaks into curved fragments. This is conchoidal fracture. Flint, quartz and glass display conchoidal fracture.</span> Description An account of the resource <em>Have a look at the<strong> rhyolite glass (<a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/7">L113</a>)</strong>, the <strong>flint nodule (<a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/35">L370</a>)</strong>, and <strong>quartz (<a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/57">M411</a>)</strong> in the 1A Reference Series.</em> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Cross-hatched twinning</h2> Subject The topic of the resource <span>Where one set of parallel twin planes intersects another at 90°, twinning is produced in a cross-hatched or tartan pattern. This is a diagnostic characteristic of microcline (an alkali feldspar), and is occasionally referred to as microcline twinning.</span> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Cryptocrystalline</h2> Subject The topic of the resource <span>Rocks with a crystalline structure in which the individual crystals are so small that they cannot be identified using standard optical microscopy are described as cryptocrystalline.</span> Description An account of the resource <em>Compare with<span> </span><a href="https://wserv3.esc.cam.ac.uk/p1acollections/items/show/227">microcrystalline</a>.</em> 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/. Description An account of the resource This glossary describes a number of geological terms with which the 1A students should become familiar.<span> It is by no means an exhaustive list, but is aimed to help you understand the material within the first year course.</span> Title A name given to the resource Glossary 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>Crystal lattice</h2> Subject The topic of the resource <span>An ordered arrangement of atoms within a solid. This typically exhibits long range order in the form of a repeating motif (unit cell) on each lattice point, to build up the whole structure.</span>