Description:
Thorite is the most common thorium mineral. Thorium
is a highly radioactive element and could be used as
a replacement for uranium in nuclear power generation.
It is estimated to be three times as common as uranium
and all the thorium in the Earth's crust could have
more potential energy than both uranium and the fossil
fuel reserves combined. Uranium and thorium are considered
to be the primary sources of the internal heat of the
Earth through their radioactive decay. Although thorite
is the most common thorium mineral, it is not the primary
ore of thorium. The phosphate mineral monazite has an
average of about 6% thorium in its composition that
includes several rare earth elements. Enough monazite
is mined to supply most of the current thorite demand.
If monazite deposits become scarce or the demand for
thorium increases, then thorite and to lesser extents
other thorium bearing minerals such as thorianite, thorogummite
, huttonite and thorutite will gain greatly in importance.
Thorite is currently an important ore of uranium. A
variety of thorite often called "uranothorite"
is particularly rich in uranium and has been a viable
uranium ore at Bancroft, Ontario, Canada. Other varieties
of thorite include "orangite", an orange variety;
"calciothorite" an impure variety with trace
amounts of calcium and "freyalite" actually
a discredited variety containing cerium (it turned out
to be an altered form of the mineral melanocerite).
There is a closely related mineral to thorite called
thorogummite that was once considered a variety of thorite
but is a product of alteration to thorite. Thorogummite
has some of the SiO4 tetrahedrons replaced by four hydroxides
for a formula that looks like: (Th, U)2(SiO4)(2 - X)(OH)4X
The X represents the conversion of one silicate tetrahedron
with a negative four charge (-4) to four hydroxides
with a negative one charge (-1) each. So that if half
the silicate tetrahedrons are replaced by the four hydroxides,
where X = 1, the formula would look like this: (Th,
U)2SiO4(OH)4 Thorite also is related to a mineral called
huttonite. Thorite and huttonite are dimorphs. The two
minerals have the same chemistry, they just have different
structures, di means two and morph means shape. A similar
situation occurs with the dimorphism of diamond and
graphite, both of whom are composed of carbon, but have
very different structures. Huttonite ironically belongs
in the Monazite Group and is related structurally to
its members. Because thorite is highly radioactive,
specimens are often metamict. This is a condition found
in radioactive minerals and results from the destructive
effects of its own radiation on its crystal lattice.
The effect can destroy a crystal lattice completely
while leaving the outward appearance unchanged. Thorogummite
is believed to be formed from thorite by hydration which
is facilitated by metamictation. Specimens of thorite
generally come from igneous pegmatites and volcanic
extrusive rocks, hydrothermal veins and contact metamorphic
rocks as well as small grains found in detrital sands.
Crystals are rare, but when found can produce nicely
shaped short prismatic crystals with pyramidal terminations.
Remember, this is a 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 ! |
