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
Streak:
Colour: Dark green-black, red-brown, nearly black
Solubility: Gelatinises in hydrochloric acid
RADIOACTIVE
Environments
Tritomite-(Y) occurs in granite pegmatites and pegmatite veins cutting
pyroxenite
(HOM).
Localities
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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