Formula: Y5(SiO4,BO4)3(OH,O,F)
Nesosilicate (insular SiO4 groups), britholite group
Specific gravity: 3.05 to 3.40
Hardness: 3½ to 6½
Colour: Dark green-black, red-brown, nearly black
Solubility: Gelatinises in hydrochloric acid


Tritomite-(Y) occurs in granite pegmatites and pegmatite veins cutting pyroxenite (HOM).


At the type locality is an unnamed prospect pit, Cardiff Township, Haliburton County, Ontario, Canada, tritomite-(Y) occurs as masses in a narrow pegmatite stringer in a vuggy pyroxenite, associated with calcite, apatite, diopside, fluorite and scapolite. Cracks in the tritomite-(Y) contain a fine-grained white carbonate high in yttrium (AM 46.1204). Other associated minerals include zircon, quartz, albite variety oligoclase, microcline, magnetite, titanite variety keilhauite, fergusonite, biotite, apatite, clinopyroxenes and amphiboles (Mindat, HOM).

At the Faraday Mine, Faraday Township, Hastings County, Ontario, Canada, tritomite-(Y) is associated with albite, calcite, arfvedsonite, pyrite, quartz and tourmaline (HOM).

Near Cranberry Lake, Sussex county, New Jersey, USA, tritomite-(Y) occurs in a granite pegmatite composed of microcline, quartz, albite variety oligoclase, magnetite, black zircon, clinopyroxene, amphibole, fergusonite, titanite variety keilhauite, apatite, tourmaline, biotite, fluorite and galena. It is intimately associated with magnetite, black zircon, apatite, and fergusonite, although it contains no niobium or tantalum and only traces of zirconium or phosphorus. Zircon found in Precambrian rocks is usually brown, red, or hyacinth in colour; it is rarely black. It would appear that this part of the New Jersey highlands is an yttrium-rich as well as a magnetite-rich province, thus, tritomite-(Y), rather than tritomite-(Ce), was formed in the pegmatites of this area. The Langesundsfjord pegmatites, which contain tritomite-(Ce), are enriched in rare earths predominantly of the cerium group (AM 47.9-25).

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