Fluorite
is a mineral with a veritable bouquet of brilliant colors. Fluorite
is well known and prized for its glassy luster and rich variety of colors.
The range of common colors for fluorite starting from the hallmark color
purple, then blue, green, yellow, colorless, brown, pink, black and
reddish orange is amazing and is only rivaled in color range by quartz.
Intermediate pastels between the previously mentioned colors are also
possible. It is easy to see why fluorite earns the reputation as "The
Most Colorful Mineral in the World".
The many colors of fluorite are truly wonderful. The rich purple color
is by far fluorite's most famous and popular color. It easily competes
with the beautiful purple of amethyst. Often specimens of fluorite and
amethyst with similar shades of purple are used in mineral identification
classes to illustrate the folly of using color as the sole means to
identify minerals.
The
blue, green and yellow varieties of fluorite are also deeply colored,
popular and attractive. The colorless variety is not as well received
as the colored varieties, but their rarity still makes them sought after
by collectors. A brown variety found in Ohio and elsewhere has a distinctive
iridescence that improves an otherwise poor color for fluorite. The
rarer colors of pink, reddish orange (rose) and even black are usually
very attractive and in demand.
Most
specimens of fluorite have a single color, but a significant percentage
of fluorites have multiple colors and the colors are arranged in bands
or zones that correspond to the shapes of fluorite's crystals. In other
words, the typical habit of fluorite is a cube and the color zones are
often in cubic arrangement. The effect is similar to phantomed crystals
that appear to have crystals within crystals that are of differing colors.
A fluorite crystal could have a clear outer zone allowing a cube of
purple fluorite to be seen inside. Sometimes the less common habits
such as a colored octahedron are seen inside of a colorless cube. One
crystal of fluorite could potentially have four or five different color
zones or bands.
To
top it all off, fluorite is frequently fluorescent and, like its normal
light colors, its fluorescent colors are extremely variable. Typically
it fluoresces blue but other fluorescent colors include yellow, green,
red, white and purple. Some specimens have the added effect of simultaniously
having a different color under longwave UV light from its color under
shortwave UV light. And some will even demonstrate phosphorescence in
a third color! That's four possible color luminescence in one specimen!
If you count the normal light color too. The blue fluorescence has been
attributed to the presence of europium ions (Eu +2). Yttrium is the
activator for the yellow fluorescence. Green and red fluorescent activation
is not exactly pinned down as of yet, but may be due to the elements
already mentioned as well as other rare earth metals; also manganese,
uranium or a combination of these. Even unbonded fluorine trapped in
the structure has been suggested. The word fluorescent was derived from
fluorite since specimens of fluorite were some of the first fluorescent
specimens ever studied. The naming followed the naming precedence set
by opalescence from opal; ergo fluorescence from fluorite.
Another
unique luminescent property of fluorite is its thermoluminescence. Thermoluminescence
is the ability to glow when heated. Not all fluorites do this, in fact
it is quite a rare phenomenon. A variety of fluorite known as "chlorophane"
can demonstrate this property very well and will even thermoluminesce
while the specimen is held in a person's hand activated by the person's
own body heat (of course in a dark room, as it is not bright enough
to be seen in daylight). The thermoluminescence is green to blue-green
and can be produced on the coils of a heater or electric stove top.
Once seen, the glow will fade away and can no longer by seen in the
same specimen again. It is a one shot deal. Chlorophane (which means
to show green) is found in very limited quantities at Amelia Court House,
Virginia; Franklin, New Jersey and the Bluebird Mine, Arizona, USA;
Gilgit, Pakistan; Mont Saint-Hilaire, Quebec, Canada and at Nerchinsk
in the Ural Mountains, Russia.
Fluorite
has other qualities besides its great color assortments that make it
a popular mineral. It has several different crystal habits that always
produce well formed, good, clean crystals. The cube is by far the most
recognized habit of fluorite followed by the octahedron which is believed
to form at higher temperatures than the cube. Although the cleavage
of fluorite can produce an octahedral shape and these cleaved octahedrons
are popular in rock shops the world over, the natural (e.g. uncleaved)
octahedrons are harder to find.
A
rarer habit variety is the twelve sided dodecahedron however it is never
seen by itself and usually modifies the cubic crystals by replacing
the edges of the cube with one flat face of a dodecahedron. The tetrahexahedron
is a twenty four sided habit that is also seen modifying the cubic habit.
But instead of one face replacing each cubic edge, two faces modify
the cube's edges. Occasionally combinations of a cube, dodecahedron
and tetrahexahedron are seen producing an overall cubic crystal with
no less that three minor parallel faces replacing each cubic edge. A
fifth form is the hexoctahedron which modifies the cube by placing six
very minor faces at each corner of the cube. Twinning is also common
in fluorite and symmetrical penetration twins, especially from Cumberland
England are much sought after by collectors.
Fluorite,
as mention above, has octahedral cleavage. This means that it has four
identical directions of cleavage and when cleaved in the right ways
can produce a perfect octahedral shape. Many thousands of octahedrons
are produced from massive or large undesirable crystals of fluorite
(hopefully!) and are sold in rock shops and museum gift shops at a small
cost. Fluorite mine workers are reported to sit down at lunch breaks
and cleave the octahedrons for the extra cash. The octahedrons are very
popular due to their attractive colors, clarity, "diamond-shaped"
and low costs, but to a serious collector they are nothing more than
"cleavage fragments".
The
origin of the word fluorite comes from the use of fluorite as a flux
in steel and aluminum processing. It was originally referred to as fluorospar
by miners and is still called that today. Fluorite is also used as a
source of fluorine for hydrofluoric acid and fluorinated water. The
element fluorine also gets its name from fluorite, fluorines only common
mineral. Other uses of fluorite include an uncommon use as a gemstone
(low hardness and good cleavage reduce its desirability as a gemstone),
ornamental carvings (sometimes misleadingly called Green Quartz) and
special optical uses.
Fluorite
is the most popular mineral for mineral collectors in the world, second
only to quartz. Every mineral collection owned by even the newest and
youngest of mineral collectors must have a specimen of fluorite. Fluorite
is by far one of the most beautiful and interesting minerals available
on the mineral markets.
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