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Prasiolite is a pale green to yellowish-green variety of quartz. Its color is typically a result of heat treatment of amethyst or yellowish quartz containing specific iron impurities. The term 'Green Amethyst' is a trade name and can be misleading, as amethyst is specifically purple quartz. Scientifically, it is known as prasiolite. It exhibits the typical properties of quartz, including a vitreous luster and conchoidal fracture.
How to Identify
- Color
- Pale green to yellowish-green. The color is generally uniform but can show slight variations.
- Luster
- Vitreous (glassy).
- Texture
- Smooth to the touch when polished; rougher in its natural crystal form.
- Crystal Form
- Typically forms in hexagonal prisms terminating with rhombohedral faces. Can also be found in massive or granular habits.
- Cleavage
- None. Quartz lacks cleavage.
- Geological Environment
- Found in igneous and metamorphic rocks, particularly in pegmatites, hydrothermal veins, and volcanic rocks where amethyst or yellowish quartz has been subjected to natural heat. Also found in alluvial deposits.
Key Facts
- Hardness: 7 on the Mohs scale
- Specific Gravity: 2.65 g/cm³
- Crystal System: Trigonal
- Color: Pale green to yellowish-green
- Luster: Vitreous
- Transparency: Transparent to translucent
- Fracture: Conchoidal
- Cleavage: None
- Composition: Silicon dioxide (SiO2)
Quick Check
- Color: Pale green to yellowish-green
- Luster: Vitreous
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic, often forming hexagonal prisms with rhombohedral terminations; also massive, granular.
- Cleavage Type: Absent (no cleavage)
- Fracture Type: Conchoidal (shell-like, curved fractures)
- Tenacity: Brittle
- Luster Type: Vitreous (glassy)
Formation
Prasiolite is typically formed when natural amethyst or yellowish quartz containing iron inclusions is heated, either naturally by geological processes (e.g., volcanic activity, geothermal vents) or artificially in a laboratory setting. The heat treatment alters the oxidation state of the iron impurities within the quartz lattice, leading to the characteristic green color. Natural prasiolite is relatively rare.
Usage
Primarily used as a gemstone in jewelry due to its attractive green color and durability. It is also collected by mineral enthusiasts.
Age Distribution
Geologically ancient, formed in various geological eras depending on the host rock formation.
Where to Find
Montezuma, Minas Gerais, Brazil
A significant source of natural prasiolite, where amethyst is naturally heated by geological processes.
Lower Silesia, Poland
Another known locality for naturally occurring prasiolite.
Thunder Bay, Ontario, Canada
Some amethyst from this region can be heat-treated to produce prasiolite.
Arizona, USA
Certain amethyst deposits can yield prasiolite upon heat treatment.
Finding Tips
Look for Amethyst Deposits
Natural prasiolite is rare. Most 'Green Amethyst' on the market is heat-treated amethyst. Therefore, searching for amethyst deposits in areas known for natural heating events (e.g., volcanic regions) might yield natural prasiolite, or at least material suitable for heat treatment.
Examine Color Uniformity
Natural prasiolite often has a more subtle and sometimes uneven green color compared to artificially treated material, which can be more uniformly colored.
Consult Geological Maps
Identify regions with known occurrences of amethyst in geological settings that suggest past or present geothermal activity, which could lead to natural prasiolite formation.
Similar Rocks
Amethyst
Amethyst (SiO2)
Also known as: Purple Quartz
Citrine
Citrine (SiO2)
Also known as: Yellow Quartz
Peridot
Olivine ((Mg,Fe)2SiO4)
Also known as: Olivine
Green Beryl
Beryl (Be3Al2Si6O18)
Also known as: Emerald (if gem quality)
Scientific Classification
- Mineral Class
- Silicate (Tectosilicate)
- Group
- Quartz Group
- Crystal System
- Trigonal
- Chemical Formula
- SiO2
- Composition
- Silicon dioxide
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