Titanite - CaTiSiO₅

Sphene is named from the greek word "sphenos" for wedge, because of its typical wedge shaped crystal habit. It is also alternatively called titanite for its titanium content. Titanite is an orthosilicate with independent SiO₄ tetrehedra united by Ti⁴⁺ in octahedral coordination and Ca²⁺ in sevenfold coordination. Al³⁺ or Fe³⁺ may partially replace Ti⁴⁺ and are most common impurity.

Titanite is a common accessory mineral in igneous rocks, being found as small crystals in granites, diorites, syenites, nephelite syenites. Also found often in crystals of considerable size embedded in the metamorphic rocks, gneiss chorite-schist and crystalline limestone. Very commonly associated with chlorite. Also found with iron ores, pyroxene, amphibole, scapolite, ziron, apatite feldspar, quartz, etc. Titanite may alter to a fine-grained aggregate of Ti-oxides such as rutile or anatase.

Optical Properties:
• Relief: High
• Color: Pale brown or pale yellow
• Interference colors: Strong but masked by the color of the mineral.
• Cleavage: Distinct prismatic on (110)
• Form: Commonly appears as diamond-shaped or wedge-shaped section.

Bibliography

• Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. Springer Science & Business Media.
• Fossen, H. (2016). Structural geology. Cambridge University Press.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005).
• Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.
• Vernon, R. H. (2018). A practical guide to rock microstructure. Cambridge university press.

Photo
Layer of titanite crystals in a amphibolite. PPL image, 10x (Field of view = 2mm)	Layer of titanite crystals in a amphibolite. XPL image, 10x (Field of view = 2mm)	Zoned titanite crystals. PPL image, 2x (Field of view = 7mm)
Zoned titanite crystals. PPL image, 10x (Field of view = 2mm)	Zoned titanite crystals. XPL image, 10x (Field of view = 2mm)	Zoned titanite crystals. XPL image, 10x (Field of view = 2mm)
Titanite and biotite crystals. Sesia-Lanzo zone, Piedmont, Italy. PPL image, 10x (Field of view = 2mm)	Twinned titanite and biotite crystals. Sesia-Lanzo zone, Piedmont, Italy. XPL image, 10x (Field of view = 2mm)	Titanite and biotite crystals. Sesia-Lanzo zone, Piedmont, Italy. PPL image, 10x (Field of view = 2mm)
Titanite and biotite crystals. Sesia-Lanzo zone, Piedmont, Italy. XPL image, 10x (Field of view = 2mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Titanite - CaTiSiO5

Titanite - CaTiSiO₅