Physical,
Chemical and Structural Properties of Amethyst, for Identification and
Classification in Geology, Mineralogy, Crystallography and Gemology
studies for professionals and Rock Collectors
This site contains
information on the Physical Properties and Chemical Composition of
Minerals, gemstones, crystals, precious metals, and sedimentary, igneous
and metamorphic rocks for crystallography, geology, identification of
minerals, Jewelry and mineralogy. This includes cleavage, description of
crystal formations, crystal structure, hardness, specific gravity, Mohs’
Scale, crystal features and crystal habits for identification and
classification purposes.
Amethyst
is an impressive variety of quartz which naturally occurs in crystal
form. These transparent prismatic crystals can be found in clusters as
an incrustation (or druse) in a nodular stone, commonly known as a
geode. Physically it is much like quartz in it's transparency and luster
but amethyst is unique in color. Ranging in shades of purple from pale
lavender/lilac to a deep intense purple, amethyst is the most valuable
form of quartz. In jewelry, the deepest most dense variations of
Amethyst that maintain their transparency are considered the most
precious.
Physical
Properties
As mentioned above, Amethyst can
vary in shades of purple and although this form of quartz must be purple
to be Amethyst, the shades can even include a reddish and milky purple
quality. The purple color comes from the existence of manganese in clear
quartz. The presence of iron in certain quantities determines the
comparative intensity of its color. Because of it's naturally
unparalleled color, Amethyst could be very expensive but due to it's
wide-spread availability and numerous global deposits, it can be found
very inexpensively. Not only can Amethyst range in color but it also
ranges in transparency from transparent to almost translucent
though always maintaining it's glassy luster. With a specific gravity of
6.5 and hardness of 7 (Mohs' scale), Amethyst is tough to distinguish
from it's synthetic imposters. In nature as a mineral, each crystallic
cluster differs from region to region. Even different mines can produce
different qualities of Amethyst. Depending upon the region and mine of a
specimen, a good majority of each individual crystal can be clear or
smoky while one end contains all the color. True gem experts can come
pretty close to identifying the region from which a particular specimen
originated from the density of it's color, the cleavage, shape, crystal
system and other physical characteristics which imply it's original
context.
Chemical
Properties
The chemical name for Amethyst,
Silicon Dioxide (SiO2), along with distinctive attributes relating to
it's color are representative of its chemical composition. As mentioned
through it's physical properties, Amethyst obtains it's color through a
combination of manganese impurities (Mn) and the existence of iron (Fe)
in specific quantities. The color of each crystal is dependant upon the
distribution of color-filled bands within it. These color bands are
stable only at temperatures below 480 degrees Fahrenheit (248.9 degrees
Celsius) so this semi-precious stone should be protected from extreme
heat in order to prevent fading. Professional heating treatments (on the
other hand) have been used on Amethyst to produce the popular gems known
as Citrine and Ametrine (400 and 500 degrees Celsius). Many of the
naturally occurring Citrines began as Amethyst and were created by being
heated by exposure to lava and magma from nearby volcanoes and other
magma containing bodies. Ametrine has become a popular semi-precious gem
which is a product of being half Amethyst and half Citrine.
Other
Characteristics of Amethyst
Index
of refraction: 1.5-1.6
Birefringence:
0.01
Mohs'
Scale Hardness: 7
Fracture:
Conchoidal
Specific
Gravity: 6.5
Crystal
System: Tetrahedral
Amethyst
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