Amethyst Chemical Properties

Amethyst Chemical Properties

by Ritika Changrani

Amethyst is a macro crystalline variety of Quartz with the chemical formula SiO2 (Silicon Dioxide). Mostly occurring as purple, lilac or mauve in colour, the purest form is colorless. Experts attribute the purple color of amethyst to small amounts of iron (Fe4+) impurities (approximately 40 parts per million) at specific sites in the crystal structure of quartz.

Once adorned on the Crown Jewels of England, Amethyst is a royal gem – a symbol of sincerity, security, spirituality and peace of mind.

A purple variety of quartz, amethyst is a semi – precious yet popular gemstone. If it were not for its abundance in nature, amethyst would be very expensive. Its royal colour makes it desirable and can be compared to the most expensive of purple crystals. So if you want a gem that is easy on your pocket and yet glamorous, amethyst is the perfect choice.

Although it must always be purple to be amethyst, it is available in an expansive array of purple shades. Intensely colored amethyst may have red flashes. It may also have color zones. By looking at its color, transparency, crystal habit, occurrence, hardness, and lack of cleavage, one can determine the authenticity of an amethyst.

In nature, amethysts appear long and prism-like with a six-sided pyramid at either end or as crystalline crusts with only the pointed terminations (druzes). The amethyst is appreciated for its imperial shades and variety of cuts that lend it a dazzling look.

A premium amethyst is purple, bluish purple to reddish purple in hue, vivid in intensity and medium dark in tone. Heating the amethyst removes the colour or converts it to yellow Citrine, depending on the site and original oxidation state of the iron impurities present and the intensity and duration of heating. The iron impurities need to be re-oxidized to return the original colour. The process is called irradiation. Irradiation may be done by two means: natural and synthetic. As a rule the process is reversible, but there are exceptions. Application of extreme or disproportionate heat may alter the existing pattern of iron impurities. In that case the amethyst is lost and cannot be retrieved by any chemical process. However, it is not possible to state whether an amethyst has undergone irradiation or not. Therefore, buying from your trusted Jeweler or getting it checked with a gemstone laboratory first, is the safest way to go.

Amethyst in its purest form is colorless and transparent. Experts are of the opinion that the rich purple colour of the amethyst is to its high content of Iron Oxide (Fe2O3) impurities. It contains more iron than any other form of quartz. Quartz makes up about 12% of the earth’s crust, making it the single most abundant mineral on earth. It is present in an extensive range of igneous, metamorphic and sedimentary rocks. Based on the size of crystals, quartz is mainly divided into two categories: macro crystalline quartz, in which the individual crystals are easily distinguishable and cryptocrystalline quartz, in which the crystals can be distinguished only under a powerful light microscope. All forms of quartz (including amethyst) are piezoelectric, which have important applications in electronics. This is a rare property, possessed by only one other gemstone called tourmaline.

Found in abundance, amethyst is a variety of macro crystalline quartz. It has been found in quartz veins and siliceous volcanic as geodes. However, it is not the same everywhere. Amethysts are unique to geographical regions or even mines. Different areas have different types of formations and iron distribution patterns. Experts can often identify the source mine that a particular amethyst came from. The key to this is the color, shape of crystal, inclusions, associations and formation of the amethyst.

Properties At A Glance:

Mineral Quartz
Chemical Composition SiO2 (Silicon Dioxide)
Class Tectosilicate
Colour Clear, Lilac, Mauve, Purple, Rose
Luster Vitreous
transparency Transparent to Translucent
Crystal System Hexagonal-R; 32 (Trigonal-Trapezohedral)
Hardness 7
Specific gravity 2.65
Index of Refraction 1.54-1.55
Birefringence 0.009
Cleavage None
Pleochroism Distinct
Fracture Conchoidal

The characteristic hardness of amethyst makes it an ideal choice for almost any type of jewelry setting. Normal plating and pickling solutions do not alter its nature. While it poses no significant problems, care must be taken while soldering, as amethyst is sensitive to sudden temperature changes. A persistent or sudden application of heat could cause a crack or colour alteration in the gem.

The amethyst is sufficiently durable and can be worn confidently without worry. It does not break easily due to absence of cleavage planes. However, sharp blows must be avoided. Clean your amethyst with warm water, soap and a soft bristle brush. Extended exposure to sun must be avoided or else the gem will become pale.

Amethyst is the trendiest purple gemstone. Its distinctive colour complements almost any complexion and wardrobe. Designers advocate amethyst as the chic choice for jewelry because of its regal hue, affordability, and variety in sizes, shapes and tones.

Since no two amethyst crystals are alike in colour or composition, its uniqueness makes it a covetable gem. So go ahead and get yours!

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