Amethyst has been known as the
most highly prized form of quartz. The color can vary from a pale
purple to a dark purple. Very often the color is unevenly distributed and is
most intense at the tips of the crystals. Amethyst owes its color to the presence of
iron built into its crystal lattice [3]. Some of this iron sits in sites
normally occupied by silicon and some is interstitial. The iron impurity is
usually in the +3 valence state to substitute Si. For natural amethyst, Gamma ray radiation [1]
[2] from nuclear decay in the surrounding rocks can make charge transfer from
an iron lattice site to an interstitial iron, and form +4 valence state of iron
(purple color centers). This +4 iron absorbs certain wavelengths (357 and 545
nanometers) of light causing the purple color. It is needed to have quartz that
contains the right amounts of iron and then is subjected to enough natural
radiation to cause the color centers to form.
The most famous and
commercially important amethyst locations are in volcanic rocks. Amethyst is
also found in igneous, and certain metamorphic rocks, as those contain enough
radioactive trace elements for a sufficient irradiation of the crystals. As the iron is built into the crystal
lattice, amethyst is sometimes found in ore deposits. Sometimes amethyst
banded with purple and white lines.
Amethyst is crystalized Silicon
Dioxide belong to hexagonal crystal group, its moderate refraction and its
weight in common with the other quartzes. Amethyst’s Hardness is 7, and can be melted at 1650 degree and is insoluble
in common solvents. It has been known that the amethyst changes its color on
being heated above 250 degree due to charge transfer from iron +4 valence
states to +3 valence states, and the color become darker under irradiation due
to more charge transfer from iron +3 valence states to +4 valence states.
Synthetic amethyst can be
produced by irradiation of clear quartz to form iron +4 valence state (purple color centers),
and the clear quartz has been first doped with iron impurities. On exposure
higher temperature above 250 degree, the irradiation effects can be partially
cancelled and the amethyst generally becomes yellow or even green.
Amethyst is a very common
mineral and is found worldwide. The deposits with the greatest economic
significance are in various states in southern Brazil and in Uruguay. The third major export country is Madagascar.
Good amethyst was found in Aztec graves, though the deposits from which they
were extracted are no longer known today. On the Canadian side of Lake Superior
in North America, there is a place named Amethyst Harbor. The violet quartz is
found there in ample quantities, though rarely in gemstone quality.
Brilliant purple amethyst gemstone
beads are an eye-catching choice for jewelry. Romantic and passionate
amethyst, the traditional birthstone for those born in February, is said to
represent courage and inner strength. Amethyst gemstone jewelry makes a
thoughtful and personal birthday gift.
High quality amethyst is
cut to maximize the intensity of its color. Amethyst is also formed into stone beads with different
shapes: round, coin, oval, square, pillow, cube, tube, et al. With
amethyst beads in your favorite
color and shape, you even can create your own unique piece of amethyst jewelry, and with plenty of
opportunity to customize to fit your unique style. There are plenty of low-cost
amethyst beads available through
online store and be sure to check out the discounted amethyst beads first to start your design.
Do not expose an amethyst to
direct sunlight for a long time. Very likely it will pale out by the
ultraviolet radiation. Some amethyst pales out really quickly and some very
slowly, but you can't tell in advance. Thus amethyst jewelry should not be worn
while sunbathing, and sudden changes of temperature can also be harmful to the amethyst.
[1] G.R. Rossman, “Colored
varieties of the silica minerals”, Reviews in Mineralogy, Vol.29
[2] Nassau, K. (1975a) The origins of color in minerals and gems. Lapidary J., 29, 920-8, 1060-70, 1250-8, 1521.
[3] E.F. Holden, The cause of
color in smoky quartz and amethyst, American Mineralogist, Vol.9, 203-252,
1925
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