THE MINERAL EUXENITE
- Chemical Formula: (Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)2O6,
Yttrium Calcium Erbium Lanthanum Cerium Uranium Thorium Niobium Tantalum
- Class: Oxides
- Uses: A minor ore of rare earth elements and uranium, sometimes
cut as a gemstone
and as mineral specimens.
Euxenite, which is sometimes named euxenite-(Y) (the Y is for the yttrium),
is a mineral that is sometimes called a "trash can mineral" .
Because it will accommodate a wide variety of elements in its crystal structure,
generally the elements that other minerals do not seem to want, ie the
"trash". For euxenite, these elements are in a group called the
rare earths and are sometimes quite valuable, making euxenite a potentially
profitable ore. Euxenite's name is from a Greek phrase meaning "hospitable",
another reference to its . . . accommodating nature.
Euxenite is in a series with the mineral polycrase,
another "trash can mineral". Polycrase is simply richer in titanium
as opposed to the niobium rich euxenite. The other elements can be found
in both minerals and the structure is basically the same.
Because of the rare earths metals in its structure, euxenite is one
of several so called Rare
Earth Oxides. Other rare earth oxides such as
have very similar properties to euxenite and are often associated with
each other, compounding the problem. Even the common oxide,
is almost indistinguishable from these rare earth oxides without chemical
tests when rutile is found massive.
Euxenite is found in rare earth rich, granite pegmatites, a slow cooling
igneous intrusive rock. Euxenite is associated with
and other rare earth minerals. Euxenite is used as an ore for its rare
earth metals and uranium. But it is its gemstone
use that is what is odd about this mineral. Like
euxenite is sometimes cut into attractive gems and used as cabochons, although
since the stones are slightly radioactive, their use as wearable gemstones
should be quite ...well...risky!
Euxenite is an interesting and at times attractive mineral. Although
most crystals are embedded and do not show good form, some crystals are
exceptional and can demonstrate a high luster. Remember, this is a slightly
radioactive mineral and should be stored away from other minerals that
are subject to damage from radioactivity and of course human exposure
should be limited !
Color is black with a tinge of yellow, brown or green.
Luster is greasy to submetallic.
Transparency: Crystals are opaque.
Crystal System is orthorhombic; 2/m 2/m 2/m
Crystal Habits include tabular to prismatic crystals with domal
terminations and often embedded in the matrix of the host pegmatite; as
well as granular and massive.
Cleavage is absent.
Fracture is conchoidal.
Hardness is 5.5 - 6.5
Specific Gravity is approximately 4.3 - 5.9 (heavy for non-metallic
minerals). Extreme variation caused by variable composition of component
Streak is yellow, brown or gray.
Other Characteristics: Slightly radioactive and crystals/specimens
are often coated with a yellow limonite
like earthy coating.
Associated Minerals include quartz,
Notable Occurrences include the Ural Mountains of Russia; Iveland,
Aust-Agder, Norway; Sweden; Minas Gerais, Brazil; Ampangabe, Madagascar;
Quadeville, and Madwaska, Ontario, Canada; sites in the White Tank Mountains
and Kingman Quarry, Arizona; Encampment, Wyoming and in Colorado, USA.
Best Field Indicators are luster, fracture, color, radioactivity,
associations, environment and specific gravity.