THE RARE EARTH OXIDES
GROUP OF MINERALS
The Rare Earth Oxides Group is sometimes referred to as just the Rare
Earths or sometimes as REO. This group of minerals is purely an informal
group as most official mineral groups are related first by structural similarities
and secondly by chemistry. There are no structural characteristics to this
group as a whole. The reason for this group is because of the chemical
and general physical property similarities that exist in most rare earth
First, the chemical similarities. All members of this group are members
of the Oxide Class and contain, as a significant portion of their
chemistries, members of the so called rare earth elements.
Rare earth elements
or rare earth metals are all part of a series in the Periodic Table of
Elements called the Lanthanide Series that runs from atomic number 57 to 71.
In addition the elements yttrium #39, thorium #90 and scandium #21
are also considered to be rare earth metals because they share similar
properties. Uranium, although often associated with rare earth metals,
is not technically a rare earth metal.
There are many uses for rare earth metals.
They are constantly being used in the nuclear power and nuclear weapons industries for both practical and experimental utilization.
Some rare earth metals have found more down to earth applications in metallurgy, ceramics, glass making, dyes, lasers, televisions and other electrical components.
The movie industry makes use of several rare earth metals to help produce the high intensity lamps that are needed for movie projectors.
Yttrium has been used for decades in a
diamond simulant called YAG or yttrium aluminum garnet which has physical properties similar to natural
garnets but with a brilliance and fire more similar to diamond.
The importance of rare earth metals is most certainly on the rise.
The rare earth metals were given this nickname because they were thought to be extremely rare in the Earth's crust.
Now many of them are thought to be as common an element as silver.
Dispite this, as the label implies, these metals are rare in the Earth's crust or
more accurately they are rarely concentrated enough to be mined in large quantities.
The reason for this rarity of concentration is that these elements are
incorporated into other commoner minerals as mere traces with far too
low of concentrations to be used as ores.
There is no good concentrating effect as there exists with other valuable metals.
Oxygen seems more capable than other negatively charged ions to round these
metals up when they are concentrated above normal levels.
This makes the rare earth oxides all that more valuable.
The rare earth oxide minerals share some general physical properties.
They tend to be black or dark brown in color with reddish, yellowish or more commonly
brownish streaks. They are nearly opaque to opaque with a few exceptions
of translucent specimens. A variation of resinous, pitchy or submetallic
luster is usually found within each rare earth oxide's range of luster
possibilities as these lusters are not too different from each other. Rare
earth oxides are relatively hard (5 - 6.5). They commonly have a very characteristic
conchoidal fracture. Their higher than average specific gravities within
each species range considerably from 3.5 to 7 and up; the variation is
due to the large amount of substitution of constituent elements that these
minerals allow. And finally, rare earth oxides will usually have a coating
of an earthy surface alteration, which should not be removed if present
as it is part and parcel of the mineral.
As can be guessed, it is sometimes difficult to distinguish most of the rare earth oxides from one another, but identifying them as rare earth oxides is fairly easy.
These are some of the minerals of the informal Rare Earth Oxides