Amethyst

SiO2

Amethyst, a captivating purple variety of quartz, has been treasured for its beauty and symbolism for centuries. With the chemical formula SiO₂, amethyst gets its colour from trace amounts of iron. Heat treatment during formation or subsequent geological events gives rise to its violet hues, which range from soft lavender to deep purple. Known for its hexagonal crystal system, amethyst has a Mohs hardness of 7, making it suitable for jewellery that can withstand everyday wear.

Historically, amethyst was revered by ancient civilisations, from the Greeks, who believed it prevented intoxication, to European royalty, who wore it as a symbol of wisdom and power. Brazil, Uruguay, and Zambia are key sources of amethyst, with each region offering distinct colour profiles due to geological variations. Under magnification, amethyst often displays unique internal characteristics such as colour zoning and chevrons, which are needle-like inclusions. A popular choice for the February birthstone, it is linked to calm, clarity, and spiritual growth. Despite its resilience, amethyst can fade if exposed to intense sunlight for extended periods.

Facts

Mohs Hardness: 7
Refractive Index (RI): 1.544 – 1.553
Specific Gravity: Around 2.65
Fluorescence: Typically none, though some stones may exhibit weak red under longwave UV light.

Testing

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Refractometer

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Polariscope

Shows as doubly refractive with a uniaxial figure, often appearing as a hexagonal outline in polarised light.

Dichroscope

Weak pleochroism, usually from purple to a bluish or reddish tint.