<![CDATA[1A Collections]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?page=9&sort_field=added&sort_dir=d&output=rss2 Tue, 09 Apr 2024 21:22:43 +0100 p1acollections@esc.cam.ac.uk (1A Collections) Zend_Feed http://blogs.law.harvard.edu/tech/rss <![CDATA[Euhedral]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/189

Title

Euhedral

Subject

A crystal displaying its characteristic crystal form is called euhedral.

Description

See: porphyritic andesite (L130)
]]> Fri, 21 Jun 2019 15:44:06 +0100 <![CDATA[Equant]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/188

Title

Equant

Subject

A crystal which is of roughly equal size in all directions is described as equant. Although this description implies that equant crystals tend towards a spherical form, the term describes both rounded and angular crystals.

Description

See: ultramafic cumulate (L171)
]]> Fri, 21 Jun 2019 15:39:14 +0100 <![CDATA[Eolian]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/187

Title

Eolian

Description

See aeolian.
]]> Fri, 21 Jun 2019 15:37:56 +0100 <![CDATA[Dull [lustre]]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/186

Title

Dull [lustre]

Subject

Minerals displaying little or no lustre are described as dull. The surfaces of these minerals comprise coarse granulations, which scatter light in all directions. Clay minerals, for example, have dull lustre.

Description

See: adamantine
]]> Fri, 21 Jun 2019 15:37:02 +0100 <![CDATA[Crystal lattice]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/185

Title

Crystal lattice

Subject

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.
]]> Fri, 21 Jun 2019 15:35:48 +0100 <![CDATA[Cryptocrystalline]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/184

Title

Cryptocrystalline

Subject

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.

Description

Compare with microcrystalline.
]]> Fri, 21 Jun 2019 15:31:20 +0100 <![CDATA[Cross-hatched twinning]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/183

Title

Cross-hatched twinning

Subject

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.
]]> Fri, 21 Jun 2019 15:24:33 +0100 <![CDATA[Conchoidal fracture]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/182

Title

Conchoidal fracture

Subject

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.

Description

Have a look at the rhyolite glass (L113), the flint nodule (L370), and quartz (M411) in the 1A Reference Series.
]]> Fri, 21 Jun 2019 15:24:05 +0100 <![CDATA[Colour index]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/181

Title

Colour index

Subject

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:

]]> Fri, 21 Jun 2019 15:20:43 +0100 <![CDATA[Cleavage]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/180

Title

Cleavage

Subject

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°. 

]]> Fri, 21 Jun 2019 15:16:13 +0100