Sphene

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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
Green sphene from Madagascar.
Photo courtesy of Scott Davies, americanthai.com


Sphene image gallery

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.

Contents

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.

Diagnostics

Color

Yellow, brown, green, reddish.
Color is caused by rare earth elements (didymium) for yellow stones and chromium for the intense green chrome sphene.

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.

A strong doubling of facets is seen in cut stones.

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

Moderate to strong trichroism.
Yellow to brown stones: colourless, greenish-yellow, reddish.

Spectroscope

Sometimes a spectrum can be seen.
Mean absorption lines: 586, 582. Sphene may show (weak) rare earth spectra due to didymium.

Fluorescence

None (probably due to iron content).

Varieties

  • Chrome sphene, intense green (color caused by chromium).
  • Greenovite, a reddish variety owning its color to manganese (MnO) impurities.

Treatments

Sphene is changed to red or orange through heating.

Durability

Sphene's relative low hardness makes it vulnerable to abbrasion.

Occurrence

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

Facet-grade sphene was found in Mulla Ghani Baba in Mohmand Agency, NW of Peshawar, Pakistan, in 2004. The color of this sphene is medium to dark brown, and a significant 'red flash' was notable in the faceted gems. In Badadkshan, Afghanistan, sphene was also found in 2004. The color of Afghan sphene is greenish yellow. While India also produces fine sphene, Madagascar remains the main source for facet-grade sphene. While brown stones from Madagascar can be large, the green stones are most prized by gem collectors and connoisseurs.

Other deposits:
Myanmar, Sri Lanka, Brazil, Mexico, Russia and Austria

Sources

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