Amethyst – Crystal Wiki
The purple variety of quartz – one of the best-known and most popular gemstones worldwide
var. Amethyst (Quartz Group, SiO₂)
Properties & Characteristics
🔬 Scientific Data
- Chemical Formula
- SiO₂ (Silicon Dioxide)
- Crystal System
- Trigonal
- Mohs Hardness
- 7
- Density
- 2.65 g/cm³
- Refractive Index
- 1.544–1.553
💎 Physical Properties
- Color
- Purple, from pale lilac to deep purple
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Streak Color
- White
- Cleavage
- None (conchoidal fracture)
- Fracture
- Conchoidal
🌍 Occurrence
- Main Localities
- Brazil, Uruguay, Madagascar, Zambia, India
- Important Deposits
- Rio Grande do Sul (BR), Artigas (UY), Antsirabe (MG)
✨ Use & Value
- Uses
- Jewelry, collector's items, decoration
- Value Range
- Faceted stones often approx. €2–€25 per ct, high-quality collector's specimens usually approx. €30–€500+ per piece (depending on color, size, and origin).
What is Amethyst?
Amethyst is the purple variety of the mineral quartz and one of the best-known and most popular gemstones worldwide. Its name comes from the ancient Greek "amethystos" – translated "not intoxicating." In antiquity, it was believed that the stone protected against drunkenness.
Formation
Amethyst forms in volcanic rocks, mainly in cavities (geodes) of basalt and other lava rocks. Silica-rich water penetrates these cavities and crystallizes over millions of years. The typical purple color results from traces of iron (Fe³⁺/Fe⁴⁺) and natural irradiation in the rock.
Origin & Localities
The most important localities are in Brazil (Rio Grande do Sul) and Uruguay, where huge geodes with deep purple crystals are found. Other significant occurrences are in Madagascar, Zambia, and India. Brazilian amethysts tend to have lighter tones, while Uruguayan specimens often show the coveted deep purple.
Special Features
- Geodes: Amethyst geodes can grow several meters in size and sometimes weigh over a ton.
- Citrine Conversion: If amethyst is heated above 470 °C, it turns yellow-orange and becomes citrine. This rarely happens in nature – thus, most citrine on the market comes from heat-treated amethyst.
- Ametrine: A natural combination of amethyst and citrine in one crystal, almost exclusively from Bolivia.
Quality Characteristics
The most valuable amethysts exhibit a rich, even purple with a red secondary hue (so-called "Deep Siberian"). Transparency, clarity, and even color distribution determine the value. Large, flawless crystal points are particularly sought after by collectors.
Frequently Asked Questions
Is amethyst a rare stone?
Amethyst is relatively common in terms of quantity, which makes it affordable. However, high-quality specimens with deep, even purple and large size are rare and proportionally valuable – especially stones in the coveted "Deep Siberian" color quality (a trade name for deep purple with red and blue secondary tones, named after historical Siberian localities).
How can I distinguish real amethyst from fakes?
Real amethyst shows an uneven, zonal color distribution when light is shone through it. Synthetic specimens often have perfectly uniform color. Additionally, real amethyst feels cool to the touch and has a Mohs hardness of 7 – it easily scratches glass.
Does amethyst fade in sunlight?
Yes, prolonged direct sunlight can cause amethyst to fade. UV light slowly dissolves the color centers in the crystal lattice. Therefore, do not store amethyst pieces on a windowsill and protect jewelry from prolonged sun exposure.
Detailed Information
Properties & Composition
Chemical Formula: SiO₂ (Silicon Dioxide)
Crystal System: Trigonal
Mohs Hardness: 7
Density: 2.65 g/cm³
Cleavage: None (conchoidal fracture)
Luster: Vitreous
Transparency: Transparent to translucent
Streak Color: White
The purple color is caused by iron ions (Fe³⁺/Fe⁴⁺) in the quartz crystal structure, which are activated by natural gamma radiation from the surrounding rock. The color intensity depends on the iron concentration and the duration of irradiation.
Localities & Origin
Brazil (Rio Grande do Sul): Largest producer worldwide. Huge geodes, often lighter purple hues. The amethyst mines of Ametista do Sul produce geodes up to 5 meters high.
Uruguay (Artigas): Deep purple crystals of the highest quality – smaller but more intense than Brazilian ones. The geodes are often more compact with a particularly rich hue.
Madagascar: High-quality, often unusually shaped crystals with intense color and interesting phantom structures.
Zambia: Dark purple specimens with a reddish tinge, known as "African Amethyst". Often in combination with iron oxide inclusions.
India (Maharashtra): Medium-sized druses with well-formed crystals, often available as mineral points on the market.
Care & Handling
Cleaning: Lukewarm water with mild soap and a soft brush are sufficient. Do not use an ultrasonic cleaner – it can cause cracks in pre-stressed crystals.
Storage: Protect from direct sunlight! UV radiation can cause the color to fade over months. Best stored in a closed display cabinet or collection box.
Temperature: Amethyst is uncritical in a normal household. The conversion to citrine only begins at significantly higher temperatures (from approx. 470 °C) and is practically not an issue in everyday life.
Hardness: With a Mohs hardness of 7, amethyst is quite robust and suitable for everyday wear as a gemstone. Scratches from materials with higher hardness (topaz, corundum) are possible.
Uses & Applications
Jewelry: Amethyst is one of the most popular gemstones. Faceted stones are used in rings, pendants, and earrings. Cabochons show the stone in its natural beauty.
Collector's Items: Large, well-formed crystal specimens and geodes are coveted collector's items. Pieces with phantom crystals or scepter crystals, in particular, fetch high prices.
Market Pricing Logic: Small faceted amethysts are usually calculated per carat, while geodes and collector's specimens are priced per piece.
Decoration: Amethyst geodes and druses are used as natural decorative objects in living spaces. Cut geodes with polished edges are exceptional home accessories.
History: In the Middle Ages, amethyst was considered a symbol of humility and was worn by bishops as a pectoral cross. Until the 18th century, it was one of Europe's most precious gemstones.
Glossary
Important technical terms related to amethyst and quartz mineralogy.
- Ametrine (am-uh-TREEN)
A naturally occurring mixed mineral of amethyst (purple) and citrine (yellow) in a single crystal. Almost exclusively from the Anahí Mine in Bolivia.
- Druse (DROO-zuh)
A rock cavity lined with crystals – similar to a geode, but flatter and more open. Amethyst druses are popular collector's items and decorative objects.
- Geode (JEE-ohd)
A hollow cavity in volcanic rock, the inner walls of which are lined with crystals. Amethyst geodes form in basalt and can grow several meters in size.
- Crystal System (KRIS-tl SIS-tuhm)
Describes the geometric arrangement of atoms in a crystal. Amethyst belongs to the trigonal crystal system, which explains its typical six-sided prism shape.
- Mohs Hardness (MOHZ HAHRD-nes)
A scale from 1 (talc) to 10 (diamond) used to determine the scratch hardness of minerals. Amethyst has a Mohs hardness of 7, making it relatively scratch-resistant and well-suited for jewelry.
- Phantom Crystal (FAN-tuhm KRIS-tl)
A crystal in which an earlier growth phase is visible as a shadowy outline. Amethyst phantoms often show lighter or darker purple zones inside.
- Scepter Crystal (SEP-ter KRIS-tl)
A rare crystal form where a larger crystal head sits atop a thinner stem – like a scepter. One of the most sought-after forms among amethyst collectors.
Further Reading
For those who want to delve deeper:
- . "Gemstones of the World: All Types and Varieties". BLV Buchverlag (2020), pp. 118–123.
- . "Which Stone Is That?". Kosmos Verlag (2019), pp. 82–85.
- Mindat.org – Amethyst – Hudson Institute of Mineralogy. International mineral database with localities and photos.
- GIA – Amethyst Quality Factors – Gemological Institute of America. Quality criteria for amethyst (color, clarity, cut).
- Mineralienatlas – Amethyst – Mineralienatlas.de. German-language database with locality data and scientific information.
- Gemdat.org – Amethyst – Gemdat.org. Gemological data on optical properties and refractive indices.
