https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?page=25&sort_field=Dublin+Core%2CTitle&output=atom <![CDATA[1A Collections]]> 2024-04-09T21:25:50+01:00 Omeka https://wserv3.esc.cam.ac.uk/p1acollections/items/show/54 <![CDATA[<h2>Serpentine</h2>]]>

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
]]> 2019-07-04T09:52:19+01:00

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
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/252 <![CDATA[<h2>Simple twinning</h2>]]> 2019-07-04T09:53:25+01:00

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.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/253 <![CDATA[<h2>Solid solution</h2>]]> 2019-07-04T09:53:25+01:00

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.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/254 <![CDATA[<h2>Specific gravity, D</h2>]]> 2019-07-04T09:53:25+01:00

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.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/44 <![CDATA[<h2>Sphene<strong> (titanite)</strong></h2>]]>

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

]]> 2019-07-04T09:52:15+01:00

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

]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/255 <![CDATA[<h2>Splendent [lustre]</h2>]]> See metallic.]]> 2019-07-04T09:53:26+01:00

Title

Splendent [lustre]

Description

See metallic.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/256 <![CDATA[<h2>Subhedral</h2>]]> 2019-07-04T09:53:26+01:00

Title

Subhedral

Subject

A crystal displaying some, but not all of its characteristic crystal faces is called subhedral.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/257 <![CDATA[<h2>Sutured contacts</h2>]]> Have a look at the quartzites (L520, L521) in the 1A Reference Series.]]> 2019-07-04T09:53:27+01:00

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.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/258 <![CDATA[<h2>Tabular</h2>]]> 2019-07-04T09:53:27+01:00

Title

Tabular

Subject

Flat, planar, non-elongate crystals are described as having a tabular habit. Tabular crystals are thicker than platy crystals.
]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/259 <![CDATA[<h2>Tartan twinning</h2>]]> See cross-hatched twinning.]]> 2019-07-04T09:53:27+01:00

Title

Tartan twinning

Description

See cross-hatched twinning.
]]>