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Amethyst is a violet variety of quartz (SiO2) and is one of the most popular and widely recognized gemstones. Its color ranges from a light, slightly pinkish violet to a deep, rich purple. The intensity and distribution of color can vary within a single crystal. It typically forms as prismatic crystals with pyramidal terminations, often found lining the interiors of geodes or vugs. Amethyst is known for its vitreous luster and conchoidal fracture. It is a relatively hard mineral, making it suitable for everyday wear in jewelry.
How to Identify
- Color
- Ranges from pale lilac to deep violet-purple. Color can be unevenly distributed, often concentrated at the crystal tips.
- Luster
- Vitreous (glassy).
- Texture
- Smooth to slightly rough on crystal faces, depending on growth conditions.
- Crystal Form
- Typically forms as hexagonal prisms terminated by rhombohedral faces (pyramidal). Often found as drusy coatings or large crystals within geodes.
- Cleavage
- None (lacks cleavage).
- Geological Environment
- Hydrothermal veins, vugs, and geodes within igneous (especially basaltic) and metamorphic rocks. Also found in alluvial deposits.
Key Facts
- Hardness: 7 (Mohs scale)
- Specific Gravity: 2.65 g/cm
- Crystal System: Trigonal
- Color: Violet, purple, often with color zoning
- Luster: Vitreous
- Transparency: Transparent to translucent
- Fracture: Conchoidal
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with trace iron impurities
Quick Check
- Color: Purple to violet
- Luster: Vitreous (glassy)
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic hexagonal crystals, often terminated by rhombohedral faces; massive, granular, drusy coatings, geodes.
- Cleavage Type: None (lacks cleavage).
- Fracture Type: Conchoidal (shell-like, curved fractures).
- Tenacity: Brittle.
- Luster Type: Vitreous (glassy).
Formation
Amethyst forms in hydrothermal veins, geodes, and vugs within igneous rocks (especially basaltic lavas) and metamorphic rocks. The purple color is attributed to irradiation of iron impurities (Fe3+) within the quartz crystal lattice. The presence of trace amounts of iron and subsequent natural gamma-ray irradiation from surrounding rocks causes the color centers responsible for the purple hue. Heating amethyst to temperatures above 300-500 C can cause it to lose its purple color, often turning yellow (citrine), orange, green (prasiolite), or colorless, depending on the specific impurities and heating conditions.
Usage
Amethyst is primarily used as a gemstone for jewelry, ornamental carvings, and decorative items. Its attractive color and relative hardness make it popular for various lapidary applications. It is also collected by mineral enthusiasts.
Age Distribution
Amethyst forms in geological environments that can range from relatively recent volcanic activity (tens of millions of years ago) to much older hydrothermal systems (hundreds of millions of years ago). Its formation is not tied to a specific geological age but rather to the conditions present.
Where to Find
Brazil
Known for large geodes and high-quality, deep purple amethyst, particularly from the state of Rio Grande do Sul.
Uruguay
Produces some of the finest deep purple, often reddish-purple, amethyst, frequently found in basaltic geodes.
Zambia
A significant source of dark, intense purple amethyst, often with good clarity.
Russia (Ural Mountains)
Historically famous for its exceptionally fine, deep purple amethyst, often with a reddish flash.
Canada (Thunder Bay, Ontario)
Known for its distinctive reddish-purple amethyst, often found in large veins.
United States (various states)
Occurrences in Arizona, North Carolina, Georgia, and Maine, among others, though typically not as prolific as major international sources.
Finding Tips
Look for Geodes and Vugs
Amethyst commonly forms in geodes (hollow, crystal-lined rocks) and vugs (small cavities) within volcanic or metamorphic rocks. Look for rounded or irregular rock formations that might contain these cavities.
Identify Host Rocks
In many major deposits, amethyst is associated with basaltic lava flows or granitic pegmatites. Familiarize yourself with the appearance of these host rocks in your search area.
Check for Hydrothermal Veins
Amethyst can also form in hydrothermal veins, which are fractures in rocks filled with mineral-rich fluids. Look for quartz-rich veins with purple coloration.
Examine Color and Luster
The distinctive purple color and vitreous luster are key identifiers. Be aware that the color can fade with prolonged exposure to sunlight.
Test Hardness
With a Mohs hardness of 7, amethyst will scratch glass and steel. This helps distinguish it from softer purple minerals like fluorite.
Safety Precautions
Amethyst itself is not hazardous. However, when collecting in the field, always wear appropriate safety gear (gloves, eye protection, sturdy footwear) and be aware of your surroundings, especially in old mine workings or unstable rock formations. If breaking open geodes, use proper tools and eye protection to prevent injury from flying rock fragments.
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Purple Sapphire
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Also known as: Violet Corundum
Scientific Classification
- Mineral Class
- Silicate (Tectosilicate)
- Group
- Quartz Group
- Crystal System
- Trigonal
- Chemical Formula
- SiO2
- Composition
- Silicon Dioxide, with color due to irradiation of iron impurities (Fe3+).
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