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Jadeite is a pyroxene mineral with the chemical formula NaAlSi2O6. It is one of the two minerals commonly known as 'jade' (the other being nephrite). Jadeite is renowned for its exceptional toughness, making it highly resistant to breaking and chipping, which is attributed to its interlocking fibrous or granular crystal structure. It exhibits a wide range of colors, from white to various shades of green, lavender, blue, black, and brown, often with a vitreous to greasy luster. Its formation is indicative of specific high-pressure, low-temperature metamorphic conditions.
How to Identify
- Color
- Highly variable, including white, various shades of green (from pale to emerald green, often mottled), lavender, blue, black, brown, and orange. The most prized color is an intense, translucent emerald green, known as 'Imperial Jade'.
- Luster
- Vitreous to greasy, sometimes pearly on cleavage surfaces.
- Texture
- Typically fine-grained, compact, and interlocking fibrous or granular, contributing to its exceptional toughness. Can appear massive.
- Crystal Form
- Rarely forms distinct crystals; usually found as massive, granular, or fibrous aggregates. When crystals are present, they are typically prismatic with a square or rectangular cross-section.
- Cleavage
- Perfect prismatic cleavage in two directions at approximately 87 and 93 degrees, characteristic of pyroxenes. However, due to its interlocking fibrous nature, cleavage is rarely observed in hand specimens and it tends to fracture conchoidally or unevenly.
- Geological Environment
- Found in high-pressure, low-temperature metamorphic rocks, specifically blueschist and eclogite facies. It occurs in serpentinite-associated metasomatic rocks, often in veins or lenses within serpentinite bodies, or as part of metamorphic rock assemblages in subduction zones.
Key Facts
- Hardness: 6.5-7 on Mohs scale
- Specific Gravity: 3.30-3.38
- Crystal System: Monoclinic
- Color: White, green (various shades), lavender, blue, black, brown, orange
- Luster: Vitreous to greasy
- Transparency: Translucent to opaque, rarely semi-transparent
- Fracture: Splintery to uneven, sometimes conchoidal due to its toughness
- Cleavage: Perfect prismatic on {110} at 87 and 93, but rarely observed in massive forms
- Composition: Sodium aluminum silicate
Quick Check
- Color: Variable (white, green, lavender, black, etc.)
- Luster: Vitreous to greasy
- Streak: White
Physical Characteristics
- Crystal Habit: Typically massive, granular, or fibrous aggregates; rarely as distinct prismatic crystals.
- Cleavage Type: Perfect prismatic {110} at nearly 90 degrees (87 and 93), but rarely seen due to aggregate nature.
- Fracture Type: Splintery to uneven, occasionally conchoidal.
- Tenacity: Extremely tough (resistant to breaking and chipping).
- Luster Type: Vitreous to greasy.
Formation
Jadeite forms under specific conditions of high pressure (typically >10 kbar) and relatively low temperature (200-500 C) within subduction zone environments. It is a characteristic mineral of blueschist and eclogite facies metamorphic rocks. It commonly forms from the metasomatic alteration of serpentinite or other ultramafic rocks, where sodium-rich fluids interact with aluminum- and silicon-rich protoliths. It can also form directly from the metamorphism of Na-rich sediments or igneous rocks.
Usage
Primarily used as a gemstone, particularly for carving and jewelry. High-quality, translucent green jadeite (Imperial Jade) is highly prized. It has been historically used for tools, weapons, and ceremonial objects by various cultures, particularly in Mesoamerica and East Asia, due to its exceptional toughness.
Age Distribution
Formed during high-pressure, low-temperature metamorphic events, often associated with subduction zones. Ages vary depending on the specific orogenic event, ranging from Mesozoic to Cenozoic.
Where to Find
Myanmar (Burma)
The primary source of gem-quality jadeite, particularly the highly prized 'Imperial Jade'. Found in the Uru River region of Kachin State.
Guatemala
Historically significant source, particularly for Mesoamerican cultures. Deposits are found in the Motagua Fault Zone.
Japan
Occurs in Itoigawa, Omi, and Kotaki regions, often associated with serpentinite bodies.
Russia
Found in the Polar Urals and Khakassia regions.
California, USA
Occurs in several localities, including Clear Creek, San Benito County, and along the Franciscan Complex.
Kazakhstan
Known for some jadeite occurrences.
Italy
Found in the Western Alps, associated with high-pressure metamorphic rocks.
Finding Tips
Geological Context
Focus on areas known for high-pressure, low-temperature metamorphic rocks, especially blueschist and eclogite facies, and serpentinite belts. Jadeite is often found in association with serpentine, glaucophane, lawsonite, and omphacite.
River Gravels and Alluvial Deposits
Many significant jadeite deposits are found as alluvial boulders and pebbles in riverbeds, having been eroded from their primary sources. Look for dense, smooth, often water-worn stones.
Density Test
Jadeite has a relatively high specific gravity (3.30-3.38). If you find a suspected piece, its weight will feel surprisingly heavy for its size compared to common rocks.
Hardness and Toughness
While its hardness (6.5-7 on Mohs scale) is moderate, its exceptional toughness means it is very difficult to break or chip. This can be a distinguishing feature from softer look-alikes.
Visual Inspection
Look for characteristic colors and a fine-grained, often translucent to opaque texture. The 'orange peel' texture on polished surfaces can be indicative of jadeite's interlocking granular structure.
Distinguishing from Nephrite
Jadeite is generally harder (6.5-7 vs. 6-6.5 for nephrite) and has a higher specific gravity (3.30-3.38 vs. 2.90-3.03). Jadeite also tends to have a more vibrant color range and a finer, more granular texture compared to nephrite's often fibrous, splintery appearance.
Similar Rocks
Nephrite
Nephrite (Ca2(Mg,Fe)5Si8O22(OH)2)
Also known as: Mutton Fat Jade
Serpentine
Mg3Si2O5(OH)4 (general formula)
Also known as: Bowenite, Antigorite, Chrysotile
Hydrogrossular Garnet
Ca3Al2(SiO4)3-x(OH)4x
Also known as: Transvaal Jade
Chrysoprase
SiO2 (a variety of chalcedony)
Also known as: Australian Jade
Scientific Classification
- Mineral Class
- Silicate
- Group
- Pyroxene Group
- Crystal System
- Monoclinic
- Chemical Formula
- NaAlSi2O6
- Composition
- Sodium aluminum inosilicate
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