Titanite (Sphene) Occurrence and Compositon Titanite, commonly called sphene, is an often overlooked accessory mineral in igneous and metamorphic rocks. Less commonly, it is found in sedimentary rocks. Identification Titanite is one a few minerals with very high relief and very high order interference colors. When visible, its sphenoid or wedge-shaped crystals are diagnostic. Important properties  ·Appearance and habit - The characteristic euhedral crystals, if present, are shaped like diamonds, wedges, or distorted hexagons. Typically appears as small accessory grains that stand out from other minerals.  ·Color - nearly colorless but sometimes appears brownish or gray due to high refractive index.  ·Relief - relief is very high.  ·Interference colors - extreme birefringence yields very high order interference colors that may appear white. Because birefringence is so high, interference colors don't really change when the accessory plate is inserted.  ·Interference figure - biaxial (+), 2V = 23o to 50o, but figures are hard to obtain. Similar minerals  ·Monazite, a rare phosphate mineral, is similar in some ways to titanite but has lower order interference colors.  ·Epidote has lower relief and birefringence and greater 2V.

Titanite (sphene) in a Quartz Monzonite from Garfield, Colorado This view shows a titanite "wedge" surrounded by magnetite, quartz and feldspar, and minor epidote and chlorite. The titanite has very high relief and its interference colors are of such high order that they are hard to identify. The "wedge" or diamond shape of this grain is typical for titanite when it is euhedral (in many rocks it is not). Just above and to the right of the titanite is a compound grain composed of epidote (high order blue-orange-red interference colors) and chlorite (green in PP, nearly extinct in XP). Also present are three grains of magnetite (opaque). The field of view is about 2.5 mm.

Titanite (sphene) in a Quartz Monzonite from Garfield, Colorado This view shows a titanite crystal surrounded by quartz (clear, low relief, first order white to gray interference colors) and plagioclase that looks like quartz, but shows some typical plagioclase twinning (black and gray stripes). The titanite has very high relief and its interference colors are of such high order that they almost appears brown or gray. The shape of this grain is typical for euhedral titanite. The field of view is about 2.5 mm.

Garnet, Omphacite and Titanite in an Eclogite These photos show a large euhedral garnet (isotropic, in the lower left of view) in a sea of mostly omphacite (a high pressure sodic pyroxene), titanite, and a few flakes of white mica. The garnet is slightly altered to chlorite along its edges; note the anomalous interference colors in the XP view. The omphacite is pale green (PP) with interference colors that range up to first order red (XP). In a few places, where higher-order colors can be seen, the omphacite is being replaced by hornblende. The titanite crystals are small, have very high relief (PP), and appear as irregular elongate grains, some of which have acute terminations. Several flakes of white mica are present -- they are the clearest grains visible in the PP view. This specimen is from Sonoma County, California. The field of view is about 1.5 mm across.