Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Green Selenite is a variety of the mineral gypsum (hydrous calcium sulfate) characterized by its translucent to transparent nature and a distinct green hue. It typically forms in well-crystallized masses, often exhibiting characteristic tabular, prismatic, or acicular crystal habits. Its softness and perfect cleavage are key identifying features.
How to Identify
- Color
- Ranges from pale mint green to deep emerald green, often translucent.
- Luster
- Vitreous (glassy) to pearly on cleavage surfaces.
- Texture
- Smooth to slightly fibrous, often with visible crystal faces.
- Crystal Form
- Commonly tabular, prismatic, or acicular crystals. Can also form in 'desert rose' aggregates or fibrous masses (satin spar).
- Cleavage
- Perfect in one direction (pinacoidal), distinct in two others, leading to easy splitting into thin, flexible sheets.
- Geological Environment
- Evaporite deposits, sedimentary basins, caves, and sometimes as a secondary mineral in hydrothermal veins or altered volcanic rocks.
Key Facts
- Hardness: 2 on the Mohs scale
- Specific Gravity: 2.31 - 2.33 g/cm³
- Crystal System: Monoclinic
- Color: Colorless, white, gray, yellow, brown, green (due to inclusions)
- Luster: Vitreous to pearly
- Transparency: Transparent to translucent
- Fracture: Conchoidal to uneven
- Cleavage: Perfect on {010}, distinct on {100} and {101}
- Composition: Hydrous Calcium Sulfate (CaSO4·2H2O)
Quick Check
- Color: Pale to deep green
- Luster: Vitreous to pearly
- Streak: White
Physical Characteristics
- Crystal Habit: Tabular, prismatic, acicular, massive, fibrous (satin spar), granular, lamellar, rosettes (desert rose)
- Cleavage Type: Perfect in one direction ({010}), distinct in two others ({100} and {101})
- Fracture Type: Conchoidal to uneven
- Tenacity: Sectile (can be cut with a knife), flexible in thin sheets
- Luster Type: Vitreous to pearly
Formation
Green Selenite, like other selenite varieties, forms primarily through the evaporation of saline waters (e.g., ancient seas, playa lakes, sabkhas). The green coloration is typically due to the inclusion of microscopic particles of other minerals, most commonly copper-bearing minerals (e.g., malachite, chrysocolla) or iron silicates (e.g., chlorite, celadonite) during its crystallization. It can also form from the hydration of anhydrite (CaSO4).
Usage
Primarily used as an ornamental stone, for metaphysical practices, and as a collector's specimen. Due to its softness, it is not suitable for industrial applications requiring durability.
Age Distribution
Formed throughout geological history, particularly in sedimentary basins from the Paleozoic to Cenozoic eras.
Where to Find
Naica Mine, Chihuahua, Mexico
Famous for its giant selenite crystals, though green varieties are less common than clear ones, some inclusions can impart color.
Utah, USA
Various evaporite deposits can yield selenite, with some exhibiting green hues due to mineral inclusions.
Morocco
Known for various gypsum forms, including 'desert roses' which can sometimes have green tints.
Australia
Evaporite basins, particularly in arid regions, can host selenite deposits, some with color variations.
Finding Tips
Look for Evaporite Environments
Focus on areas with ancient or modern evaporite deposits, such as dried lake beds, sabkhas, and sedimentary rock formations that indicate past marine or lacustrine environments.
Check for Associated Minerals
Green Selenite often forms alongside other evaporite minerals like halite, anhydrite, and other gypsum varieties. The presence of copper-bearing minerals or iron silicates in the surrounding rock might indicate the potential for green coloration.
Observe Crystal Habits
Selenite typically forms distinct crystals. Look for transparent to translucent, often tabular or prismatic crystals, or fibrous masses. The green color will be an additional distinguishing feature.
Test Hardness and Cleavage
Gypsum is very soft (Mohs 2) and can be scratched with a fingernail. Its perfect cleavage allows it to be split into thin, flexible sheets, which is a key diagnostic test.
Similar Rocks
Green Calcite
Calcite (CaCO3)
Also known as: Green Iceland Spar
Prehnite
Prehnite (Ca2Al2Si3O10(OH)2)
Also known as: Grape Prehnite
Serpentine
Mg3Si2O5(OH)4
Also known as: Antigorite, Lizardite, Chrysotile
Scientific Classification
- Mineral Class
- Sulfates
- Group
- Gypsum Group
- Crystal System
- Monoclinic
- Chemical Formula
- CaSO4·2H2O
- Composition
- Calcium Sulfate Dihydrate
Explore Green Selenite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.