Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Prasiolite is a green variety of quartz, a silicate mineral. Most prasiolite available on the market is produced by the heat treatment of amethyst or yellowish quartz, primarily from Brazil and Poland. Natural prasiolite is much rarer and is found in locations such as Montezuma, Brazil, and Thunder Bay, Canada. Its color ranges from pale yellowish-green to a deeper, more vibrant green. It is often confused with other green gemstones like peridot or green tourmaline, but its specific gravity, hardness, and optical properties distinguish it.
How to Identify
- Color
- Pale yellowish-green to deep green. The color is generally uniform, but can sometimes show subtle zoning.
- Luster
- Vitreous (glassy).
- Texture
- Smooth to the touch when polished; rougher in its natural crystal form.
- Crystal Form
- Typically occurs as prismatic hexagonal crystals, often terminated with rhombohedral faces. Can also be found in massive or granular forms.
- Cleavage
- None (conchoidal fracture).
- Geological Environment
- Natural prasiolite is found in hydrothermal veins, pegmatites, and volcanic rocks where amethyst has been subjected to natural heating. Artificially produced prasiolite originates from amethyst-bearing deposits.
Key Facts
- Hardness: 7 on the Mohs scale
- Specific Gravity: 2.65 g/cm³
- Crystal System: Trigonal
- Color: Green
- Luster: Vitreous
- Transparency: Transparent to translucent
- Fracture: Conchoidal
- Cleavage: None
- Composition: Silicon dioxide (SiO2)
Quick Check
- Color: Green (pale to deep, often yellowish-green)
- Luster: Vitreous
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic hexagonal crystals, often terminated by rhombohedral faces; also massive or granular.
- Cleavage Type: None, due to its strong covalent bonds.
- Fracture Type: Conchoidal, producing smooth, curved surfaces resembling broken glass.
- Tenacity: Brittle
- Luster Type: Vitreous (glassy)
Formation
Prasiolite is typically formed by the heat treatment of amethyst or yellowish quartz. Natural prasiolite is rare and forms when amethyst-bearing rocks are heated by natural geological processes, such as intrusions or metamorphism. The green color is attributed to iron impurities within the quartz crystal lattice, which change their oxidation state upon heating.
Usage
Primarily used as a gemstone in jewelry. Due to its attractive green color and good durability, it is often faceted for rings, pendants, and earrings. It is also collected by mineral enthusiasts.
Age Distribution
Geologically widespread, found in various ages of igneous and metamorphic rocks.
Where to Find
Montezuma, Minas Gerais, Brazil
One of the primary sources of naturally occurring prasiolite, though still rare. The amethyst from this region is known to turn green upon natural heating.
Thunder Bay, Ontario, Canada
Another known locality for natural prasiolite, where amethyst has been naturally altered to green.
Lower Silesia, Poland
A source of amethyst that can be heat-treated to produce prasiolite.
Arizona, USA
Some amethyst from certain localities in Arizona can also be heat-treated to produce prasiolite.
Finding Tips
Look for Amethyst Deposits
Since most prasiolite is heat-treated amethyst, understanding where amethyst is found is key. Look for areas with hydrothermal quartz veins, pegmatites, and volcanic rock formations.
Examine Color Carefully
Natural prasiolite often has a more subtle, sometimes slightly grayish-green hue compared to the often brighter, more uniform green of heat-treated material. However, this is not a definitive test.
Check for Inclusions
Like other quartz varieties, prasiolite can contain various inclusions. These can sometimes help in identifying its origin, though they are not specific to prasiolite itself.
Consider Geological Context
In areas known for natural prasiolite, look for evidence of past geothermal activity or igneous intrusions that could have provided the necessary heat for its formation.
Similar Rocks
Amethyst
SiO2
Also known as: Purple Quartz
Citrine
SiO2
Also known as: Yellow Quartz
Peridot
(Mg,Fe)2SiO4
Also known as: Olivine
Green Tourmaline
Complex borosilicate
Also known as: Verdelite
Prehnite
Ca2Al(AlSi3O10)(OH)2
Also known as: Grape Jade
Scientific Classification
- Mineral Class
- Silicates
- Group
- Tectosilicates (Quartz Group)
- Crystal System
- Trigonal
- Chemical Formula
- SiO2
- Composition
- Silicon dioxide with trace iron impurities responsible for color.
Explore Prasiolite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.