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Jasper is an opaque, impure, cryptocrystalline variety of quartz, chemically silicon dioxide (SiO2). It is typically red, yellow, brown, or green in color, and rarely blue. The distinctive patterns and colors are due to the presence of various mineral inclusions, often iron oxides, which can constitute up to 20% of its volume. Its microcrystalline structure gives it a fine-grained, smooth texture when polished. It is a tough and durable material.
How to Identify
- Color
- Extremely variable, commonly red, yellow, brown, green, but can be blue, black, or multicolored with distinct patterns (e.g., orbicular, banded, brecciated). The color is opaque.
- Luster
- Dull to vitreous (glassy) on fresh fracture, often waxy to dull on unpolished surfaces.
- Texture
- Smooth, fine-grained, non-granular. When broken, it exhibits a conchoidal fracture.
- Crystal Form
- Massive, cryptocrystalline (crystals are too small to be seen without high magnification). Does not form macroscopic crystals.
- Cleavage
- None. Exhibits conchoidal fracture.
- Geological Environment
- Found in association with volcanic rocks (e.g., rhyolite, basalt), in hydrothermal veins, as infillings in sedimentary rocks, and as replacement minerals in various rock types. Often occurs in nodules, concretions, or as vein fillings.
Key Facts
- Hardness: 6.5-7 on the Mohs scale
- Specific Gravity: 2.58-2.91 (typically around 2.65-2.66)
- Crystal System: Trigonal (cryptocrystalline aggregates)
- Color: Opaque, highly variable (red, yellow, brown, green, blue, black, multi-colored)
- Luster: Dull to waxy, sometimes vitreous on fresh fracture
- Transparency: Opaque
- Fracture: Conchoidal to splintery
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with various mineral inclusions
Quick Check
- Color: Opaque, highly variable (red, yellow, brown, green, multi-colored)
- Luster: Dull to waxy, sometimes vitreous on fresh fracture
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, cryptocrystalline aggregates, nodules, concretions, vein fillings
- Cleavage Type: None
- Fracture Type: Conchoidal to splintery
- Tenacity: Tough
- Luster Type: Dull, waxy, sometimes vitreous
Formation
Jasper forms when silica-rich solutions, often hydrothermal, precipitate microcrystalline quartz and other mineral phases within voids, fractures, or as replacements of other materials. The characteristic colors and patterns are due to inclusions of iron oxides (hematite, goethite), clay minerals, and other fine-grained impurities. It can form in various environments, including volcanic settings, sedimentary basins, and areas of hydrothermal alteration.
Usage
Historically, Jasper has been used for tools, weapons, and ornamental objects. Today, it is primarily used as an ornamental stone, for cabochons, beads, carvings, and other lapidary purposes. Its diverse colors and patterns make it popular in jewelry and decorative arts.
Age Distribution
Found in geological formations ranging from Precambrian to Cenozoic, depending on the specific deposit type.
Where to Find
United States
Oregon (Picture Jasper), Idaho (Bruneau Jasper), California (various types), Arizona, Washington.
Australia
Pilbara region (Mookaite Jasper), various other localities.
India
Known for various colors and patterns.
Madagascar
Produces orbicular and other patterned jaspers.
Russia
Ural Mountains (Orsk Jasper).
Egypt
Historically significant source of red jasper.
Finding Tips
Look for associated geology
Jasper is often found in areas with past volcanic activity, hydrothermal alteration, or in sedimentary layers where silica-rich fluids have permeated.
Examine riverbeds and gravels
Jasper is durable and often survives weathering and transport, making it a common find in alluvial deposits.
Check for opaque, fine-grained material
Unlike crystalline quartz, jasper is opaque and lacks visible crystal faces. Its fracture will be smooth and conchoidal.
Observe color and pattern
The wide range of colors and distinctive patterns are key indicators. Look for reds, yellows, browns, and greens, often with banding, orbicular structures, or brecciated textures.
Similar Rocks
Chert
Chalcedony (a variety of microcrystalline quartz)
Also known as: Flint
Agate
Chalcedony (a variety of microcrystalline quartz)
Also known as: Banded Chalcedony
Opal
Hydrated amorphous silicon dioxide (SiO2·nH2O)
Also known as: Hydrated Amorphous Silica
Scientific Classification
- Mineral Class
- Silicates (Tectosilicates)
- Group
- Quartz Group (Chalcedony Subgroup)
- Crystal System
- Trigonal (microcrystalline aggregates)
- Chemical Formula
- SiO2 (with various impurities)
- Composition
- Silicon dioxide with inclusions of iron oxides, clay minerals, and other fine-grained materials.
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