Preface
This
month, we are learning more about recent gemstone favorite: Spessartine Garnet.
From gem shows to jewelry stores, and in the field, this highly prized sparkly wonder may
keep our minds reminiscent on the summer sun, or on autumn pumpkins.
Our exploration is more on the lab characteristics and some world locales. Let's
go!
Introduction
Welcome to
another Mineral-of-the-Month
installment!
Our focus this
month is on a specific garnet: Spessartine Garnet. Spessartine or
spessartite garnet is one of many gems found in the garnet family.As bright orange
crystals
in nature, and as a prized gemstone of the new millennium, it has a universal
appeal. Our
author this month is Karissa Hendershot, a professional geographer, avid fossil and
mineral
collector, and accomplished lapidary.
Enjoy!
Spessartine
Garnet
By
Karissa Hendershot
 (Photo
source: gemstone.org)
Garnets are a common mineral found
in many metamorphic rocks. It is also sometimes found in
pegmatites dikes and as grains in sedimentary deposits. The name garnet comes from the
Latin
word granatus which means "like a grain" in reference to the crystal form. There
are many types
of garnets as the chemistry varies widely. The name spessartine comes from the locality of
Spessart, Germany. Spessartines are often brownish or brown-red. The other types of
garnets
are: andradite, grossular, pyrope, almandine, and uvarovite.
The fantastic found of an up to then extremely rare
Garnet variety puzzled experts all over the world
some years ago. On the Kunene River, on the border between Namibia and Angola, there was
the
surprising and spectacular discovery of bright orange to red Spessartine, which was
originally named
after their occurrence in the German Spessart Mountains. Until the legendary mine was
discovered in
Namibia, Spessartines had existed as mere collector’s items or rarities. They were
hardly ever used
for jewelry because they were so rare. But the new find changed the world of jewelry
gemstones.
From this time on, an exceptionally fine and brightly orange-red gemstone has completed
the offered
range. The trade name "Mandarin-Garnet” was coined, and the wonderfully orange colored Fine
Garnet
became world-famous almost over night. Unfortunately the mine in the remote Namibian
mountains
could only be exploited for a few years. Prospecting for the gemstones in the isolated
bush land
became more and more complicated and expensive It had to be expected, then, that the very
upstart
among the quality gemstones would only be available in limited amounts from the stocks of
few
cutters. However, another sensation was caused by discovering another occurrence of the
orange-colored treasures, this time in Nigeria. In color and brilliance they are so
similar to the
Namibian stones that only experienced experts will be able to tell them apart. (Source: gemstone.org)
The garnet group of
minerals show crystals with a habit of rhombic
dodecahedrons and trapezohedrons.
They are nesosilicates with the same general formula, A3B2(SiO4)3 in which the A site is usually
occupied by divalent cations (Ca, Mg, Fe2+) and the B site by trivalent cations (Al, Fe3+,
Cr). The
chemical elements in garnet
include calcium, magnesium, aluminium, iron2+, iron3+,
chromium,
manganese, and titanium. Garnets show no cleavage and a dodecahedral parting. Fracture is
conchoidal to uneven; some varieties are very tough and are valuable for abrasive
purposes. hardness
is 6.5-7.5, specific
gravity is 3.1-4.3, lustre is vitreous to resinous,
and they can be transparent to
opaque. (Source: About.com)
Spessartine is
one of the aluminum garnets, along with almandine and pyrope forming the
"pyralspite" group. (The calcium or "ugrandite" garnets consist of
uvarovite, grossular and andradite.)
Its ideal composition is Mn3Al2(SiO4)3, with the silica groups (SiO4) being isolated, not
linked in
chains or sheets as in most silicate minerals. Almandine and pyrope have iron (Fe) and
magnesium (Mg), respectively, instead of the manganese (Mn). (From Wikipedia,
the free
encyclopedia)
The formulas and names of common garnet species are:
Some rare species of garnet are known that illustrate the wide range of
substitution that the garnet
crystal structure can accommodate. They include:
 (Source:
Publication
#sp14-95)
There are a number of trade
and variety names for garnet, most of these names are for particular
colors of a specie. Malaya or Mandarin is a trade name for a pyrope-spessartite that
varies in color
from red, through shades of orange and brownish orange to peach and pink. Natural
Spessartine
is orange in color, but iron impurities are usually
present, giving it a reddish or brownish color.
Hessonite is the variety name for a fine orange, cinnamon brown, or pinkish variety of
grossularite,
while tsavorite is the trade name for fine dark green grossularite. Melanite is a black
titanium
bearing variety of andradite and demantoid is a rich green variety. Rhodolite is a
purplish red
pyrope-almandite solid solution garnet. Fine-quality pyrope garnets from Czechoslovakia
are
often called Bohemian garnets. Almandite and almandite-pyrope solid solution garnets are
the
best abrasive types, but andradite, grossularite, and pyrope also are used. All species of
garnet
have been used as gemstones.. Spessartine itself is not a common garnet, and is not
usually
found as transparent, gem quality material.
Some other locations not listed above include Iskardu, Pakistan; Sri
Lanka; Sanyeshan,
Guangdon Province, China; Broken Hill, New South Wales, Australia; and Berilanda, Ceara,
Brazil.
Notable localities
in the United States include:
(Source: About.com)
California
Some of the finest quality spessartite garnet known come
from pegmatites in San Diego County.
Spessartites have been found on Gem Hill near Mesa Grande and in mines in the Rincon and
Pala Districts. The most productive area with the finest quality garnets is on the western
side of
Hatfield Creek Valley near Romona. Near Indian Head Hill in San Diego County is a deposit
of
fine-quality hessonite garnet, and another deposit is near Dos Cabezas.
Colorado
Faceting-grade spessartite garnets can be found in the gas
cavities in the rhyolite flow on
Ruby Mountain near Nathrop, Chaffee County.
Nevada
An alluvial deposit of almandite garnet is found along
Hampton Creek Canyon in White Pine
County about 3 km from the mouth of the canyon. No production history is available for the
deposit. The source of the garnet is quartz-garnet-mica-staurolite schist that forms a
portion
of the walls of the canyon.
Spessartine garnets can be found at Ely and several other
locations in White Pine County.
Most of the dark brown crystals are of interest only as specimen, but a few will cut very
small clear stones.
Pennsylvania
Leiper's quarry, Avondale, Delaware Co., Pennsylvania (mindat.org)
Utah
Thomas Range, Juab Co.
Virginia
Two mines in Amelia County account for the majority of the
production of gem-quality garnet,
they are the Morefield and Rutherford. The Spessartine from these mines, primarily the
Rutherford, are etched-crystal masses and fragments, not individual perfect crystals. The
pieces
range from pea size to as large as a grapefruit. In 1991, a single piece, dubbed the
Rutherford Lady,
was found that weighed more than 2,800 carats. Color varies from a fantastic light pure
orange,
almost yellow to shades of red-orange, red, and brownish-red, but the orange overtone
always
is present.
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Spessartine garnet on Albite matrix,
Little Three Mine, Ramona, San Diego County, California
Photo by and Courtesy of Isaias Casanova |
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Spessartine Garnet,
Pederneira Mine, Minas Gerais, Brazil
Photo by and Courtesy of Isaias Casanova |
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Spessartine on Microcline,
Tongbei, Yungxiao County, Fujiang, China
Photo by and Courtesy of Isaias Casanova |
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Spessartine on Smoky Quartz,
Tongbei, Yungxiao County, Fujiang, China
Photo by and Courtesy of Isaias Casanova |
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Spessartine with Muscovite,
Tongbei area, Yungxiao County, Fujiang, China
Photo by and Courtesy of Isaias Casanova |
|
Spessartine with Smoky Quartz on Orthoclase,
Tongbei, Yungxiao County, Fujiang, China
Photo by and Courtesy of Isaias Casanova |
Spessartine
Garnet, University of Delaware
Garnet Fact Sheet
Spessartine Garnet at mindat.org
Garnet, Emporia State
University
Alan Guisewhite's
Spessartine Garnet Page
Here is where DMS Members can add their
Spessartine Garnet photos to share with us.
Until Next Time
We hope you have enjoyed our all too short visit to
Spessartine Garnet. Please join us next month,
for another article, and we shall journey together!
Until then, stay safe, and happy collecting. 
Article Contributors
I would like to gratefully acknowledge the generous
contributions of our fellow Spessartine Garnet
enthusiasts, collectors, authors, curators, professionals, and club members who made this
work
possible. Thanks.
© 2006 All contributions to this
article are covered under the copyright protection of this article
and by separate and several copyright protection(s), and are to be used for the sole
purposes of
enjoying this scholarly article. They are used gratefully with express written
permission of the
authors, save for generally-accepted scholarly quotes, short in nature, deemed legal to
reference
with the appropriate citation and credit. Reproduction of this article must
be obtained by express
written permission of the author, Kenneth B. Casey, for his contributions, authoring,
photos, and
graphics. Use of all other credited materials requires permission of each
contributor separately .
Links and general contact information are included in the credits above,
and throughout this article.
The advice offered herein are only suggestions; it is the reader's charge to use the
information
contained herein responsibly. DMS is not responsible for misuse or
accidents caused from this
article. All opinions, theories, proofs, and views expressed within this article, and in
others on this
website, do not necessarily reflect the views of the Delaware Mineralogical Society.
Suggested Reading
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About the Author: Karissa is the current President of the Delaware
Mineralogical Society. She is also a member of the Tuscarora Lapidary Society (TLS),
and is an accomplished lapidarist and collector. She also has
affiliations with other mineral and fossil clubs in the eastern United States, and
encourages folks of all ages on the enjoyment of our hobby.
E-mail: kdhendershot@delminsociety.net |
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