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Gemstones are timeless treasures of nature that not only
represent objects of beauty and intrigue, but also are some
of the more valuable commodities on earth. The extraordinary
and satiated colors of many gems enhance their aesthetic
beauty, while others yield extraordinary fire, birefringence
or other unique light displays. When mankind first picked a
stone from the ground for its innate beauty rather than as a
tool or weapon, this symbolized an important event in
evolution. Mankind visualized beauty. When this stone was
given to another as a gesture of friendship or love - a
unique quality of the human soul was manifested in the
sharing.
These events led man to search for similar rocks and
minerals. The recognition of certain characteristics in a
particular stone and its association with nearby specific
rock types, such as agate or jasper in distinct grey to
white rock (limestone), or quartz crystals in vugs of milky
white and pink rocks (granite pegmatite), etc., greatly
enhanced the ability of early prospectors to find additional
decorative stones and gems. Recognition of such associations
signaled the start of the science of prospecting. As time
passed, these primitive prospectors exchanged ideas and
concepts that ultimately led to the science of geology.
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Some gems have favorable characteristics that allow survival
during weathering, erosion, stream-transportation and
concentration. Gems may be found in igneous, metamorphic,
and/or sedimentary rocks and typically are associated with
specific rock types and mineral suites. Unlocking these
characteristics and clues can lead to the discovery of
additional deposits.
Gemstones are sought for personal adornment and have become
the prized possessions of men, women, kings and queens. Some
of the more exotic minerals and gems represent the most
valuable commodities on earth based on size. For example, a
62-carat royal blue rectangular cut sapphire valued at
US$2.8 million ($45,000/carat, or >9,000 times more valuable
than an equivalent weight in gold). In general, rubies are
more valuable. In 1998, a Burmese ruby of 15.97 carats sold
at a Sotheby's auction for US$3.63 million ($227,301/carat).
More recently (2005), Christie's of New York sold a near
perfect 8.01-carat Burmese ruby for US$2.2 million - a
record per carat price for a ruby (US$274,656/carat)! Some
jade specimens of unimaginable value have included a
1.4-inch long jadeite cabochon that sold for US$1.74
million. In 1999, a jadeite bangle only 2 inches in length
and 0.3 inch wide sold at a Christie's auction in Hong Kong
for US$2,576,600. Even more incredible was a 27-bead
emerald-green jadeite necklace, known as the Doubly
Fortunate that sold in Hong Kong for US$9.3 million in 1997.
Some of the more valuable diamonds are red and pink fancies.
A small 0.95-carat purplish-red diamond (the Hancock Red)
sold for nearly US$1 million. To put this in perspective,
one carat weighs only 0.2 gram (0.007 ounce). Thus, this
diamond was valued at more than 200,000 times an equivalent
weight in gold - a common value for flawless pink diamonds.
Other priceless treasures have been purchased by royalty or
donated to royal treasuries. Most notable were those cut
from the Cullinun rough, the largest diamond ever found at a
whopping 3,106 carats. The extraordinary gems faceted from
this rough were donated to the British royalty and reside in
the British
crown jewels.
Many gemstones have intrinsic properties that make them
visually attractive: others stimulate our imaginations with
unique qualities. The value of others has reached
extraordinary heights due to ingenious marketing strategies
such as a group of former industrial diamonds that are now
coveted by the wealthy. These include brown and very light
brown diamonds that were at one time considered to be almost
worthless, but today are marketed as rare cognac and
champagne diamonds of great demand. Yellow diamonds, also
once considered low-value stones, are marketed as Canaries.
Others, such as Zoisite, an alteration mineral, have been
brilliantly marketed as Tanzanite.
Tapping into geological knowledge allows geologists and
prospectors to predict where gemstones will be found and in
what types of host rock they will occur. Such information
can lead to significant discoveries, such as the extremely
rich diamond deposits in the Canada in the 1990s, the
discovery of major poly-gemstone deposits
(iolite-ruby-sapphire-kyanite) in Wyoming, discovery of one
of the largest opal deposits in North America as well as
several other gemstones in the Wyoming Craton over the past
2 to 3 decades.
In future articles, I will discuss methods I've used
successfully to find a variety of gem, near gem and lapidary
deposits over the past few decades and tell you how you can
use similar methods to find gemstone deposits.
Recommended Reading
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Hausel, W.D., 2005, Minerals
and Rocks of Wyoming: A Guide for Collectors,
Prospectors and Rock Hounds: Wyoming Geological Survey
Bulletin 72, 159 p.
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Hausel, W.D., 2005, Geologists
Locate Giant Gemstones: ICMJ’s Prospecting and Mining
Journal 74:7, 7-9.
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Hausel, W.D., 2006a, Gemstone
discoveries in Wyoming: Rocky Mountain Association of
Geologists Outcrop 55:3.
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Hausel, W. D., and Sutherland,
W.M., 2000, Gemstones and other unique minerals and
rocks of Wyoming - a field guide for collectors. Wyoming
State Geological Survey bulletin 71.
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Kievlenko, E.Y. 2003. Geology
of Gems. Ocean Publications Ltd., Littleton, CO. 432.
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Krajick, K. 2001. Barren Lands.
Times Books, Hery Holt, New York.
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Walton, L., 2004. Exploration
criteria for Coloured Gemstone Deposits in the Yukon.
Yukon Geological Survey Open File Report 2004-10. 184.
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