Amethyst: Characteristics And Properties
Amethyst is a variety of silicon quartz, characterized by its unique purple hue. Amethyst is one of the most well known semi-precious gems in the world, favored by lapidaries for its soft vibrant color, natural abundance, and relatively high durability.
Amethyst has also played a role in a number of cultures through history, often being used for decorative, religious, and medicinal purposes.
Amethyst is found in many places over the world, generally forming in high-temperature location from igneous, sedimentary, and metamorphic rock deposits. Most of the amethyst mined currently comes from South America; in particular from Brazil and Uraguay where amethyst crystals are found in underground cavities formed from basalt flow.
The porous basalt absorbs water with dissolved amounts of silicon and other minerals. Over time, the intense heat and pressure form the crystal from the initial watery solution. The gem is associated with the zodiac sign Pisces and it is the birthstone of February.
History of Amethyst
Amethyst has been used by a number of societies throughout history. Archaeological evidence indicates that the ancient Egyptians favored amethyst, often using it for decorative and clothing purposes. Due to the wine-like color of amethyst, the Greeks associated the stone with Bacchus, the Greek god of wine.
The Greeks believed that amethyst could prevent intoxication, as reflected in their practice of carving cups from the gem. In fact, the name “amethyst” comes from the Greek words a-“not” and methysko-“intoxicate.” In 1522 the French poet Remy Belleau invented a classical style myth about the origins of amethyst, meant to represent the Greeks’ attraction to the stone. The myth goes that the god Bacchus was pursuing a mortal woman Amethyste, who rebuffed his affections.
Amethyste prayed for chastity to the goddess Diana, who in return turned her into a white stone. Humbled by Diana’s fortitude and desire to remain chaste, Bacchus poured wine over the stone as an offering, staining it purple and creating the first amethyst.
The Romans were fond of the stone and would use it to create elaborate relief carvings. In the middle ages, Amethyst was used in Europe as a talisman of protection and a symbol of status. Soldiers believed that the stone would keep them safe and level-headed during battle and Anglican bishops wore a ring made from the stone; a reference to the description of the Apostles as “not drunk” at Pentecost in Acts 2:15.
Up until about the 18th century, amethyst was listed as one of the most valuable and sought-after gemstones, along with diamonds, sapphires, rubies, and emeralds. However, both the relatively recent discovery of vast natural deposits of amethyst and technological advances in the process of mining have driven the value down exponentially. In spite of this, the highest grade variants of amethyst, sometimes called “Deep Russian”, manage to still net an impressive price among private collectors.
Properties Of Amethyst
Like all species of quartz, amethyst is primarily composed of a tetrahedral crystalline lattice of SiO4 molecules. Also like all varieties of quartz, amethyst crystals exist in two chiral forms, a normal “right-handed” structure and a “left-handed” structure that forms spontaneously under high temperatures.
The characteristic purple hue of amethyst is due to the irradiation of iron cations (Fe3+) in the crystalline structure of the gem. Gamma radiation from the surrounding rock deposits irradiates the forming amethyst crystal, replacing the iron cations in the structure with silicon atoms. Incidentally, the susceptibility of amethyst to radiation is one of the reasons that its color will fade if left out in the sunlight for too long. Also, the natural color of an amethyst crystal can be changed through heat treatment to be lighter or darker.
Amethyst is a piezoelectric material, indicating that it can convert mechanical energy into electrical energy. The application of mechanical stress deforms the crystal’s molecular structure and creates a net difference in the distribution of electric charges. The difference in electrical potentials creates a voltage across the crystal. Piezoelectric materials like amethyst have found a number of uses in televisions, microphones, generators, and even nanotechnology.
Amethyst is also a dichroic crystal, meaning that differently polarized beams of light will have different absorption coefficients. Essentially, the molecular structure of amethyst will absorb light if it is perpendicular to the main axis of formation but will refract light if it is polarized parallel to the main axis. In some specimens of amethyst, this difference in absorption coefficients will actually result in the crystal taking on different colors depending on the polarization and angle of light passing through it. This is a property known as pleochroism.
There is a particularly rare variant of amethyst, known as ametrine. Ametrine is a variety of bicolor quartz where citrine and amethyst combine to form a single crystal. The differences in color of ametrine are due to differences in the oxidization of ferric molecules in the structure of the crystal. A temperature gradient over the crystal during formation causes different parts of the crystal to be irradiated differently, which results in the bicolor sheen of ametrine.
Famous Amethyst Specimens
Amethyst is a naturally abundant material, so it is not normally considered expensive or particularly luxurious. That being said, there is a handful of extremely famous and highly desired amethyst pieces in the world. An example is a piece known as Hephzibah’s Pendulum, made out of a faceted 34ct amethyst hanging from a brooch made of rubies, pearls, and gold.
Another extremely famous piece of amethyst jewelry is the Duchess of Windsor’s Amethyst Necklace. The necklace consists of 28 individual amethyst crystal set upon a base of 24-karat gold, surrounded bead os turquoise. It was acquired by the Duke of Windsor and gifted to his wife the Duchess in 1947.