Difference between revisions of "Sphene"

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Sphene is isostructural with tilasite, malayaite and fersmantite.
 
Sphene is isostructural with tilasite, malayaite and fersmantite.
  
==Diagnostocs==
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==Diagnostics==
  
 
===Colour===
 
===Colour===

Revision as of 11:07, 30 May 2007

Sphene
Chemical composition CaTiOSiO4
Crystal system Monoclinic
Habit Wedge shaped, massive
Cleavage Distinct, prismatic
Fracture Conchoidal
Hardness 5.0-5.5
Optic nature Biaxial +
Refractive index 1.880-2.099
Birefringence 0.100-0.135
Dispersion High, 0.051
Specific gravity 3.45-3.55
Lustre Resinous to sub-adamantine
Pleochroism Distinct to strong

Sphene is the older name of this mineral wich refers to its crystalshape. Titanite is the universial name amongst mineralogists today and refers to its content of titanium. Greenovite is the name given to red or pink sphene. Gemologists use the name sphene for gem material titanite.

Sphene is isostructural with tilasite, malayaite and fersmantite.

Diagnostics

Colour

Yellow, brown, green, reddish.

Streak

White.

Diaphaneity

Transparent to opaque.

Refractometer

nα = 1.843 - 1.950, nβ = 1.870 - 2.034, nγ = 1.943 - 2.110 with a birefringence of 0.100 - 0.192.
Optical nature: biaxial positive.

Polariscope

Due to its small to moderate 2V value (17-40°) a clear biaxial interference pattern may be seen (two melatopes visible in one image).

Pleochroism

Strong; colourless, greenish-yellow, reddish.

Spectroscope

Mean absorption lines: 586, 582.

Fluorescence

None (probably due to iron content).

Occurence

Sphene is a common and widespread mineral in many igneous rocks and metamorphic rocks. Associated minerals are pyroxene, amphibole, feldspar and quartz.

Habit

Wedge-shaped crystals that may show parting due to twinning. Less common massive or lamellar. Sphene is normally fine grained but occacionally forms large crystals.

Sphene may show some degree of metamictization.

Treatments

Sphene is changed to red or orange through heating.

Deposits

Myanmar, Sri Lanka, Brazil, Mexico, Russia and Austria

Sources

  • Gems sixth edition (2006) - Michael O'Donoghue ISBN 0750658568
  • Gemstones of the world 13th edition (2006) - Walter Schuman ISBN 1402740166
  • Mineralogy second edition (2002) - Dexter Perkins ISBN 0130620998