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Sphene Mineral Facts:

Chemical Formula: CaTiSiO₅   Sometimes known as Titanite.

Colors: Brown, black, gray, green, yellowish, sometimes rose pink or white.
Its streak is white or pink.

Hardness: 5 to 5.5
Hardness varies somewhat depending on formation and impurities.

Density: 3.4 to 3.55

Cleavage: Prismatic cleavage {110} distinct; a parting on {100} may also be present.

Crystallography: Monoclinic
Crystals varied in habit. Often with prominent basal plane which is steeply inclined and which in combination with short prism and pyramid faces a thin wedge-shaped crystal. Both contact and penetration twins are common.

Luster:. Vitreous or resinous and it is transparent, translucent or opaque.

Optics: (Refractive Index)  a = 1.90; b = 1.907; y = 2.034
Its refractive indices vary widely with the composition. In a specimen from St. Gothard, the indices for yellow light were: a= 1.874, B= 1.8940, y= 2.0093. It is pleochroic in yellow, pinkish and nearly colorless tints.

Composition, Structure and Associated Minerals:
Sphene is a widely spread constituent of igneous rocks where it has probably formed directly by crystallization from a molten magma, and is found in many schists and limestones that have been metamorphosed. In the latter cases it is of metasomatic origin. Calcium titano-silicate, Sphene consists of Silica 30.6%, titanium oxide 40.8%, lime 28.6%. Iron is usually present in small amounts.

Titanite, or sphene, usually occurs as crystals, but in some places in granular, compact masses and lamellar forms. Many specimens show also the presence of Fe2O3 , A12O3 , and in some cases considerable quantities of Y2O3 .

Identification and Diagnostics
Fusible at 4 with slight intumescence to a dark glassy mass. Only slightly attacked by hydrochloric acid. Fused with sodium carbonate; fusion product can be dissolved in hydrochloric acid; the solution when boiled with tin gives a violet color (titanium). With beads some varieties exhibit the reaction for manganese and all show the colors characteristic of titanium. All varieties are sufficiently soluble in HC1 to give the violet colored solution when treated with tin, and all are completely decomposed by H2SO4. Sphene is distinguished from staurolite and garnet by its crystallization and softness; from sphalerite by its greater hardness; from other similarly colored minerals by the reaction for the presence of titanium.

Occurrence, Localities and Origins:
It occurs as a minor mineral in many metamorphic and acidic intrusive rocks, under which conditions it forms during cooling. Further, it is a common decomposition product of ilmenite and rutile.A rather common accessory mineral in igneous rocks, being found as small crystals in granites, diorites, syenites, trachytes, phonolites, etc. Also found often in crystals of considerable size embedded in the metamorphic rocks, gneiss, chlorite-schist and crystalline limestone. Very commonly associated with chlorite. Also found with iron ores, pyroxene, amphibole, scapolite, zircon, apatite, feldspar, quartz, etc.

Localities. The mineral occurs so widely spread that even its principal localities are too numerous to mention here. Particularly fine crystals are found at Ala and St. Marcel, in Piedmont; at various points in the Zillerthal, Tyrol; Tavetsch, St. Gothard, etc., Switzerland; Ala, Piedmont; at Zoptau, in Moravia; near Tavistock and Tremadoc, in Wales; at Sandford, Maine; at various points in Lewis, St. Lawrence and Orange Counties, New York, principally in limestones; at Franklin Furnace, New Jersey, also in limestone; in Iredell, Buncombe and Alexander Counties, North Carolina, and near Eganville, Renfrew County, Ontario.  Fine crystal specimens, some of gem quality, come from Mexico and Brazil. The name Sphene comes from a Greek word meaning wedge - in allusion to a characteristic development of the crystals.

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