https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?tags=pegmatite&output=atom <![CDATA[1A Collections]]> 2024-04-09T21:16:23+01:00 Omeka https://wserv3.esc.cam.ac.uk/p1acollections/items/show/47 <![CDATA[<h2>Tourmaline</h2>]]>

Formula

(Na,Ca)(Mg,Fe,Mn,Li,Al)3(Al,Mg,Fe3+)6[Si6O18](BO3)3(O,OH)3(OH,F)

Structure

Ring silicate

Crystal System

Crystal system: trigonal (-)

Physical Properties

Colour in hand specimen: black
Hardness: 7

Optical Properties

Colour in plane polarised light: typically brown-green or green
Pleochroism: strongly pleochroic in many colours
Relief: moderate
Birefringence: typically 2nd order

Rock Specimens

L504 Garnet schist

Mineral Name

tourmaline
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Title

Tourmaline

Subject

Tourmaline is the only common mineral of which boron is an essential constituent. Its presence in a rock, therefore, indicates that the rock contains significant boron. 

Description

Formula

(Na,Ca)(Mg,Fe,Mn,Li,Al)3(Al,Mg,Fe3+)6[Si6O18](BO3)3(O,OH)3(OH,F)

Structure

Ring silicate

Crystal System

Crystal system: trigonal (-)

Physical Properties

Colour in hand specimen: black
Hardness: 7

Optical Properties

Colour in plane polarised light: typically brown-green or green
Pleochroism: strongly pleochroic in many colours
Relief: moderate
Birefringence: typically 2nd order

Rock Specimens

L504 Garnet schist

Mineral Name

tourmaline
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