<![CDATA[1A Collections]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?tags=pegmatite&output=rss2 Tue, 09 Apr 2024 21:16:23 +0100 p1acollections@esc.cam.ac.uk (1A Collections) Zend_Feed http://blogs.law.harvard.edu/tech/rss <![CDATA[Tourmaline]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/47

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
tourmaline_CS.jpg
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