AMETHYST FROM FOUR PEAKS, ARIZONA

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AMETHYST FROM FOUR PEAKS, ARIZONA

• Jack Lowell and John I. Koivula
• Chang Gyu Eun
• Hanyang University

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OUTLINE
The most important commercial source of
gemquality amethyst in the United States in the
Four Peaks mine Maricopa Country, Arizona.
This article provides a brief description of the
gemlogic occurrence of amethyst at the deposit
and summarizes the gemlogical properties of this
material. Specially, this article provides the
first gemlogical characterization of Four Peaks
amethyst.
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LOCATION AND ACCESS
The Four Peaks mountains at the southern and of
Mazatzal Range. The tallest, on the far left, is
known as Browns Peaks. The trail and mine are
visible in the right foreground.
The amethyst deposit is located within the Four
Peaks Wilderness area, approximately 75km
cast-northeast of Phoenix.
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LOCATION AND ACCESS
An elongate open cut can be seen from the trail
approaching the Four Peaks mine.
A short tunnel penetrates about 10m from this
entrance.
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GEOLOGY
Precambrian age metasedimentary rocks that were
intruded from below by a granitic
batholith. Amethyst mineralization occurs along
fractures and cavities in the brecciated
quartzite.
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MINING

• Carried out from surface outcrops of the
  amethyst-mineralized zone.
• Mining by open-pit methods employed hand tools
  and (unsuccessfully) a bulldozer.
• A tunnel was driven by hand to access productive
  areas of the deposit.
• A crew of three miners is working the deposit
  within the horizontal tunnel.
• Explosives are rarely used, and only to break up
  boulders when needs.
• Gem materials is taken out on foot or by
  helicopter.

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DESCTIPTION OF THE AMETHYST
The amethyst crystal display a typical morphology
for amethyst, consisting mainly of rhombohedral
faces.
Distinctive color zoning is evident in this
amethyst crystal fragment.
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MANUFACTURING AMETHYST FOR JEWELRY PURPOSES
This 68.39 ct amethyst from Four Peaks is the
largest stone from the deposit.
The non-calibrated amethyst ranges from 4 to 15
ct, fine-quality stones in the 15-20 ct range are
quite rare. The amethyst can be heated to
lighten the color. Is heated to 350-450?, about
a 50 success rate
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MATERIALS AND METHODS
Reactions to ultraviolet radiation In a darkened
room Conventional four-watt long-wave and
short-wave Ultra-Violet Products lamps. A solid
mineral inclusion Using a Raman Renishaw 1000
microspectrometer. Mid-infrared absorption
spectra at room temperature with FTIR. Chemical
analyses of the samples were obtained with a
Kevex Omicron X-ray fluorescence system.
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RESULTS AND DISCUSSION
Primary fluid inclusions. The largest inclusion
measures 0.7mm long.
Many of the primary fluid inclusions in the
amethyst sample also contained tiny anhedral
solid phases.
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RESULTS AND DISCUSSION
Veil-like patterns of secondary fluid inclusions
were commonly observed.
Where dense accumulations of reddish brown
hematite flakes were seen, the host amethyst
material tended to be a lighter pueple.
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RESULTS AND DISCUSSION
Transmitted light between crossed polarizers. The
opaque areas are dense accumulations of hematite
inclusions.
The most unusual visual feature was a white,
wedge-shaped zone that was seen oriented parallel
to the rhombohedral direction.
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RESULTS AND DISCUSSION

• EDXRF analysis
• Detect silicon (as expected for quartz)
• A weak fluorescence peak due to iron.
• IR spectra
• Not show the 3543 cm-1 peak that is
  characteristic of most synthetic amethyst
  although also seen in some natural amethyst.
• Infrared spectroscopy
• Provide additional evidence that the material is
  now laboratory grown.
• Dense accumulations of reddish brown hematite
  platelets
• Wedge-shaped fog-like ones

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CONCLUSION
This white gold jewelry features 6.89 ct Four
Peaks amethyst in the ring.
A small percentage of Four Peaks amethyst
exhibits red overtones and/or a deep reddish
purple body color. A color sometime described in
the trade as Siberian