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Chrysoprase is a beautiful, translucent to opaque variety of chalcedony, which is a cryptocrystalline form of quartz. Its distinctive apple-green to deep green color is caused by trace amounts of nickel. Unlike emerald, which owes its green color to chromium, chrysoprase's color is due to nickel silicates. It is highly valued for its vibrant color and uniform texture, making it a popular material in lapidary arts.
How to Identify
- Color
- Apple-green to deep green, often uniform, but can show slight banding or mottling. The color is typically stable, though prolonged exposure to sunlight or heat can sometimes cause fading in some specimens.
- Luster
- Waxy to vitreous (glassy) when polished, dull to waxy on rough surfaces.
- Texture
- Microcrystalline to cryptocrystalline, appearing massive and dense. Smooth to the touch when polished.
- Crystal Form
- Massive, botryoidal, reniform, or stalactitic aggregates. Individual crystals are microscopic and not visible to the naked eye.
- Cleavage
- None, due to its cryptocrystalline nature.
- Geological Environment
- Found in the weathered zones (laterites) of nickel-bearing ultramafic rocks (e.g., serpentinites, dunites, peridotites). It forms in veins and nodules within these altered host rocks, often associated with other secondary nickel minerals.
Key Facts
- Hardness: 6.5 - 7 on the Mohs scale
- Specific Gravity: 2.58 - 2.64
- Crystal System: Trigonal (as quartz, but cryptocrystalline aggregates appear massive)
- Color: Apple-green to deep green
- Luster: Waxy to vitreous
- Transparency: Translucent to opaque
- Fracture: Conchoidal to uneven
- Cleavage: None
- Composition: SiO2 (silicon dioxide) with trace amounts of nickel (Ni)
Quick Check
- Color: Apple-green to deep green
- Luster: Waxy to vitreous
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, botryoidal, reniform, stalactitic aggregates
- Cleavage Type: None
- Fracture Type: Conchoidal to uneven
- Tenacity: Brittle
- Luster Type: Waxy to vitreous
Formation
Chrysoprase forms as a secondary mineral in the weathered zones of nickel-bearing serpentinites and other ultramafic rocks. The green color is attributed to the presence of finely disseminated nickel silicate minerals, primarily garnierite (a general term for nickel-bearing serpentine or talc-like minerals) or other hydrated nickel silicates, within the cryptocrystalline quartz structure. It typically occurs as veins, nodules, or infillings in fractures and cavities.
Usage
Primarily used as a gemstone for cabochons, beads, carvings, and ornamental objects due to its attractive apple-green to deep green color and good polish. Historically, it has been used in jewelry since antiquity.
Age Distribution
Typically found in Cenozoic and Mesozoic weathered nickeliferous laterite deposits, but the chalcedony itself can form over a wide range of geological ages.
Where to Find
Marlborough, Queensland, Australia
Historically the most significant source, known for producing high-quality, vibrant apple-green chrysoprase.
Silesia, Poland
An important historical source, particularly from the Szklary mine, known for its good quality material.
Brazil
Various localities produce chrysoprase, often with slightly lighter or more yellowish-green hues.
United States (California, Oregon, Arizona)
Smaller deposits are found, often associated with serpentinite belts.
Russia (Urals)
Known for some occurrences, often associated with nickel deposits.
Tanzania
Emerging source of chrysoprase.
Finding Tips
Geological Context
Focus your search in areas known for ultramafic rock formations (serpentinites, peridotites) that have undergone significant weathering, leading to lateritization and nickel enrichment. Look for areas with historical nickel mining or exploration.
Associated Minerals
Chrysoprase is often found with other secondary minerals formed in lateritic environments, such as limonite, goethite, and other nickel silicates (e.g., garnierite). These can be indicators of potential chrysoprase deposits.
Veins and Nodules
Chrysoprase typically occurs as veins filling fractures or as nodules within the weathered host rock. Look for green-colored material contrasting with the surrounding reddish-brown laterite or dark serpentinite.
Hardness Test
As a variety of quartz, chrysoprase will scratch glass (Mohs hardness 5.5) and steel (Mohs hardness 6-6.5). This helps differentiate it from softer green minerals.
Translucency
Good quality chrysoprase is typically translucent, allowing some light to pass through, especially on thin edges. This distinguishes it from opaque green rocks.
Similar Rocks
Jadeite
NaAlSi2O6
Also known as: Jade
Nephrite
Ca2(Mg,Fe)5Si8O22(OH)2
Also known as: Jade
Serpentine
(Mg,Fe)3Si2O5(OH)4
Also known as: Bowenite (a variety)
Green Aventurine
Quartz with Fuchsite inclusions
Also known as: Indian Jade (misnomer)
Scientific Classification
- Mineral Class
- Silicates
- Group
- Tectosilicates (Quartz group, specifically Chalcedony variety)
- Crystal System
- Trigonal (microcrystalline aggregates)
- Chemical Formula
- SiO2 (with Ni as chromophore)
- Composition
- Silicon dioxide with trace nickel impurities (typically as nickel silicates like garnierite)
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