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 GEOLOGY & GEMSTONES
- GEM HUNTING PART 1
by
W. Dan Hausel
W. Dan Hausel Geological Consulting
LLC
Gilbert, Arizona 85233
danhausel@yahoo.com 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.
Recognizing rock and mineral
associations and understanding
regional geology is important in a
search for new gemstone deposits. In
this search, the successful
geologist and prospector must not
only focus on regional geology, but
must also understand past geological
environments. Like any other
mineral, gemstones grow under
specific physical and chemical
parameters. 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
- Hausel, W.D., 2005, Minerals and Rocks of Wyoming: A Guide for Collectors, Prospectors and Rock Hounds: Wyoming Geological Survey Bulletin 72, 159 p.
- Hausel, W.D., 2005, Geologists Locate Giant Gemstones: ICMJ’s Prospecting and Mining Journal 74:7, 7-9.
- Hausel, W.D., 2006a, Gemstone discoveries in Wyoming: Rocky Mountain Association of Geologists Outcrop 55:3.
- 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.
- Kievlenko, E.Y. 2003. Geology of Gems. Ocean Publications Ltd., Littleton, CO. 432.
- Krajick, K. 2001. Barren Lands. Times Books, Hery Holt, New York.
- 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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