<![CDATA[1A Collections]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?page=25&sort_field=Dublin+Core%2CTitle&output=rss2 Tue, 09 Apr 2024 21:25:50 +0100 p1acollections@esc.cam.ac.uk (1A Collections) Zend_Feed http://blogs.law.harvard.edu/tech/rss <![CDATA[Serpentine]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/54

Title

Serpentine

Subject

Serpentine is a common alteration product of olivine, produced by hydration at low temperatures.

Description

Formula

Mg3[Si2O5](OH)4

Structure

Sheet silicate

Crystal System

Crystal system: monoclinic or orthorhombic (-)

Optical Properties

Serpentine is commonly very fine-grained. It can be recognised by its textural association with olivine and by its low birefringence and habit.

Colour in plane polarised light: green 
Relief: low 
Birefringence: 1st order

Rock Specimens

L141 Gabbro 
L162 Basalt, porphyritic 
L172 Ultramafic cumulate

Mineral Name

serpentine
serpentine_CS.jpg
]]> Mon, 17 Jun 2019 15:35:04 +0100 <![CDATA[Simple twinning]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/252

Title

Simple twinning

Subject

A single twin plane, producing two twins, within one mineral grain is called a simple twin. The clinopyroxene augite can display simple twinning. Simple twins are occasionally referred to as Carlsbad twins.
]]> Fri, 21 Jun 2019 17:33:02 +0100 <![CDATA[Solid solution]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/253

Title

Solid solution

Subject

Minerals such as quartz have a discrete composition and thus one chemical formula (in this case SiO2). Other minerals can have a range of compositions between two or three end-member chemical formulae. Olivine, for example, has an end-member composition called forsterite (FeSiO4). By gradually replacing Fe atoms with Mg atoms, a continuous range of compositions can be produced ending at the Mg end-member, fayallite (MgSiO4). The range of compositions is called a solid solution.
]]> Fri, 21 Jun 2019 17:35:36 +0100 <![CDATA[Specific gravity, D]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/254

Title

Specific gravity, D

Subject

This is a measure of density. It is the ratio of the density of the substance being described (e.g. a mineral) to the density of water. Olivine has a specific density, D = 3.222, which means that olivine is 3.222 times more dense than water. Since water has a density of 1 g cm-3, olivine has a density of 3.22 g cm-3.
]]> Fri, 21 Jun 2019 17:37:44 +0100 <![CDATA[Sphene (titanite)]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/44

Title

Sphene (titanite)

Description

Formula

CaTi[SiO4](O, OH, F)

Structure

Orthosilicate

Crystal System

Crystal system: monoclinic (+)

Physical Properties

Colour in hand specimen: colourless, yellow, green, brown or black
Cleavage: one, good
Hardness: 5

Optical Properties

Colour in plane polarised light: colourless, yellow or typically brown
Pleochroism: moderate if coloured
Relief: high
Birefringence: 0.100-0.192; >4th order
Extinction: inclined
Twinning: simple twins; occasionally lamellar twins

Rock Specimens

L101 Granite 
L120 Granodiorite

Mineral Name

sphene
titanite

Advanced notes

Diamond shaped cross sections are common

Sphene_CS.jpg
]]> Mon, 17 Jun 2019 13:02:48 +0100 <![CDATA[Splendent [lustre]]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/255

Title

Splendent [lustre]

Description

See metallic.
]]> Fri, 21 Jun 2019 17:40:03 +0100 <![CDATA[Subhedral]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/256

Title

Subhedral

Subject

A crystal displaying some, but not all of its characteristic crystal faces is called subhedral.
]]> Fri, 21 Jun 2019 17:40:29 +0100 <![CDATA[Sutured contacts]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/257

Title

Sutured contacts

Subject

Usually refers to quartz grains, which have undergone partial recrystallisation, producing irregular, sutured grain boundaries.

Description

Have a look at the quartzites (L520, L521) in the 1A Reference Series.
]]> Fri, 21 Jun 2019 17:45:41 +0100 <![CDATA[Tabular]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/258

Title

Tabular

Subject

Flat, planar, non-elongate crystals are described as having a tabular habit. Tabular crystals are thicker than platy crystals.
]]> Fri, 21 Jun 2019 17:47:30 +0100 <![CDATA[Tartan twinning]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/259

Title

Tartan twinning

Description

See cross-hatched twinning.
]]> Fri, 21 Jun 2019 17:48:24 +0100