Description:
Monazite is actually three different minerals technically,
but because of a lack of great differences between them
they are referred to as one mineral, monazite. The three
monazites have differences in the percentages of their
chemical makeup and these differences are reflected
in their respective names. NAME: FORMULA:
MONAZITE-(Ce) (Ce, La, Nd, Th, Y)PO4
MONAZITE-(La) (La, Ce, Nd)PO4
MONAZITE-(Nd) (Nd, La, Ce)PO4 The differences in the
formula represent the greater percentages of certain
elements in the mineral. The first element listed in
the parenthesis is the element with the greater percentage
in the mineral; so that monazite-(La) is greatly enriched
in lanthanum, etc. Monazite-(Ce) is not only enriched
in cerium it is also by far the most common of the three
and is probably the actual mineral when one encounters
a specimen that is simply labeled monazite. The general
formula represents an aggregate formula for monazite.
Silica or SiO4, will often be present in monazite replacing
a small percentage of the phosphate groups, but this
is not typically shown in monazite's formula. Uranium
is also a trace element in some specimens. The name
monazite comes from a Greek word, monazein, which means
"to be alone". It is an apt name as it is
an allusion to the typical crystal habit of primary
origin for monazite as isolated individual crystals
in phosphatic pegmatites. Solitary crystals all alone
in a dissimilar crystalline matrix. The name does seem
to fit. Monazite is a primary ore of several rare earth
metals most notably thorium, cerium and lanthanum. All
these metals have various industrial uses and are considered
quite valuable. Thorium is a highly radioactive metal
and could be used as a replacement for uranium in nuclear
power generation. Monazite therefore is an extremely
important ore mineral. Monazite is radioactive, sometimes
highly radioactive, and 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
of the crystal unchanged. Increased metamictation will
increase the perfection of the specimens conchoidal
fracture. The radioactivity of monazite has been used
as an aid in radioactive dating. Monazite, as already
mentioned, forms in phosphatic pegmatites but is actually
a standard trace constituent in many ordinary igneous,
metamorphic and vein filling rocks. If not too metamict,
crystals of monazite are rather durable. They can be
weathered out from their host rocks and carried downstream
great distances and collect in river deposits and even
in ocean beach deposits. Their great density (specific
gravity is 4.6 - 5.7) makes it easy for the crystals
to be collected into what are called placer deposits.
Placers, as they are informally called, are deposits
where heavier objects settle while lighter objects such
as sand are constantly removed by the force of water.
This process naturally concentrates some pretty valuable
stuff. Ores such as rutile and monazite, metals such
as gold and platinum and gemstones such as diamonds,
rubies, sapphires and spinels, to name a few, are all
found in placers. Some monazite beach placers in India
alone are so rich that they could supply the entire
world's need for monazite for many years to come. Crystals
of monazite are generally simple equant to prismatic
crystals that show their monoclinic symmetry without
any pretense. Twinning is common and produces crosses
and angled reentrant crystals. Specimens of monazite
are sought after for their unique chemistry, nice monoclinic
form and some specimens are actually quite attractive.
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 ! |
