By Richard
W. Hughes
Introduction/Name
Garnet
is the name for a group of related mineral species. The gem garnets
include:
Pyralspites (aluminum) |
Ugrandites (calcium) |
Pyrope |
Mg3Al2(SiO4)3 |
Uvarovite |
Ca3Cr2(SiO4)3 |
Almandine |
Fe3Al2(SiO4)3 |
Grossular |
Ca3Al2(SiO4)3 |
Spessartite |
Mn3Al2(SiO4)3 |
Andradite |
Ca3Fe2(SiO4)3 |
In addition to the purer end members mixed
garnets such as malaia (or malaya, a pyrope-spessartite)
and grandite (a grossular-andradite mixture) exist. The purplish
pyrope-almandine mixture is called rhodolite.
The
name spessartite (a.k.a. spessartine) is derived
from Spessart, in N.W. Bavaria, Germany.
Color
Spessartite
garnet is ideochromatic, meaning that it is colored by a fundamental
element in its composition. That element is manganese, which produces
an orange color. Take away the manganese, and it would no longer be
spessartite. Thus spessartite has only one basic color – orange.
That
said, the color may be modified slightly by mixing
with iron, in the form of almandine. This produces
a deeper, more reddish coloration.
Spessartites
occur in three basic flavors. There are the light
and bright stones, which come from Nigeria, Ramona
(CA) and the deeper reddish orange stones that also
come from Nigeria. Then there are the fabulous tangerine
orange “mandarin” garnets from Namibia,
which are in a class all by themselves.
|
This fine stone is an example of a malaia
(pyrope-spessartite) garnet. Photo: Wimon
Manorotkul |
|
|
Spessartite with schorl tourmaline and clevelandite
from the Little Three mine at Ramona, San Diego County, California.
Photo: Wimon Manorotkul |
|
Lighting
Due
to its orange to red-orange color, spessartite generally looks best under
incandescent light. When buying any gem, it is always a good idea to
examine it under a variety of light sources, to eliminate future surprises.
Clarity
Spessartites
from most sources are reasonably clean. Thus eye-clean stones are both
desirable and possible. The exception is with the mandarin spessartites
from Namibia, which often contain small colorless fibers of tirodite
that give the stones a sleepy overall appearance. When only small amounts
are present, the effect can be quite beautiful, masking extinction and
allowing the beautiful tangerine orange color to shine completely across
the entire face of the gem.
|
Different levels of clarity are visible here
in these spessartite garnets from Nigeria. The oval stone at
left is eye clean, i.e., with no clarity defects visible to
the unaided eye. In the pear-shaped middle stone, obvious clarity
defects are visible, while in the trillion-shaped stone at
right, they are even more obvious. Photos: Wimon
Manorotkul |
|
Cut
Spessartites
are generally cut similar to other colored stones, with ovals, cushions,
trillions and emerald cuts being most common. The lack of pleochroism
means that orientation is not a problem and the equidimensional shape
of the rough generally provides good yields from rough to cut. Cabochon-cut
spessartites are also seen on occasion, particularly with the Namibian
mandarin spessartites, which tend to be more heavily included.
|
This unusual purple pyrope-spessartite mixed
garnet is in the private collection of William Larson. Most
pyrope-spessartites, which are also known as malaia garnets)
are orange in color. Photo: Wimon
Manorotkul |
|
Prices
The
prices of spessartite are, like any gem, dependent on quality. Still,
we can make a few generalizations. The flood of Nigerian spessartite
took what was once essentially a collector's stone into the realm of
jewelry staple. Nigerian spessartites typically retail for $100–250/ct.
in the smaller, 1–4 ct. range, while stones of 15–20
cts. may reach as much as $900/ct. at the retail level.
Prices
for the rare mandarin spessartites from Namibia are
even higher, with smaller goods (1–2 cts.)
fetching up to $800/ct. and fine stones above 5 cts.
extending well above $1000/ct. The largest fine mandarin
garnet seen at Pala was a super 8-ct. stone priced
at $2400/ct. retail.
|
This mandarin spessartite from Namibia shows
why this type is the most valuable of all spessartites. Photo: Wimon
Manorotkul |
|
Stone
Sizes
While spessartites of greater than 100 cts. cut
are known from both Brazil and Madagascar, fine gems of more than
15–20 cts. are rare. For mandarin garnets from Namibia, fine
gems of greater than 5 cts. are scarce.
|
These three gems illustrate the three most
important sources of spessartite garnet. From left, a mandarin
garnet from Namibia, a spessartite from Nigeria, and a spessartite
from the Little Three mine at Ramona, CA. Photos: Wimon
Manorotkul |
|
Sources
Gem
spessartite has been found at a number of localities around the world,
including Brazil, Burma, Madagascar, Mozambique, Namibia, Nigeria,
Sri Lanka and the USA (San Diego County, CA and Amelia Court House,
VA). Of these sources, the most important today are Nigeria and northeast
Namibia, in the vicinity of the Marienfluss River.
|
|
Most mandarin garnets
from Namibia have a sleepy appearance. This is due to numerous
small crystal and needle inclusions (above). Even in relatively
clean stones, graining is often strong (below). Photos: Richard
Hughes |
|
Enhancements
Unlike
many colored stones, spessartites are not currently enhanced by any
method.
Imitations
Spessartine
has never been synthesized, but a number of imitations exist, including
natural stones such as hessonite garnet, and man-made imitations such
as glass.
|
These different flavors of Nigerian spessartite
garnet. Most expensive are the rich red-oranges at right, but
what is most beautiful is an individual choice. Photos: Wimon
Manorotkul |
|
Properties
of Spessartite (Spessartine) Garnet
Composition |
Spessartite
garnet has the following composition:
Mn3Al2(SiO4)3 |
Hardness
(Mohs) |
7
to 7.5 |
Specific
Gravity |
4.15
(+ 0.05; - 0.03) |
Refractive
Index |
1.810 (+ 0.004; - 0.20) |
Crystal
System |
Isometric;
usually occurs as massive pebbles or dodecahedra/icositetrahedra
combinations |
Colors |
Due to its ideochromatic nature, spessartite
is always some shade of orange. The color is caused by manganese |
Pleochroism |
None |
Dispersion |
0.027 |
Phenomena |
Pyrope-spessartite
mixed garnets containing vanadium have been found that display
a dramatic green (daylight) to red (incandescent light) change
of color. Such stones come from East Africa and Sri Lanka |
Handling |
Ultrasonic: generally
safe, but risky if the gem contains liquid inclusions
Steamer: not safe
The best way to care for spessartite is to clean it with warm, soapy
water. Avoid exposure to heat or acids |
Enhancements |
None |
Synthetic
available? |
No |
The Collector Gem Buying Guides
In addition to the above, please visit the Learning
Vault at Palagems.com for many additional articles on gems, minerals and mining.
|