Banded Chert (River Rock)
Microcrystalline Quartz (Chert/Jasper variety) · Mineral Specimen / Decorative Stone / Industrial Mineral
Crystal System
Trigonal (Microcrystalline/Cryptocrystalline); habit is massive, typically appearing as rounded nodules or water-worn pebbles.
Mineral Group
Silicates (Tectosilicate subgroup)
Chemical Formula
SiO2 (Silicon Dioxide) with impurities of iron oxides and clay minerals
Formation Process
Sedimentary. Formed through the accumulation of silica-rich biogenic remains (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids in marine environments.
About This Crystal
An opaque, water-worn pebble approx 3cm in length. It displays prominent parallel banding in shades of tan, beige, and grey. The luster is dull to sub-vitreous, and the surface is smooth but matte due to fluvial erosion.
Physical Characteristics
Color: Tan and grey bands; Streak: White; Cleavage: None; Fracture: Conchoidal to splintery; Specific Gravity: 2.6-2.65; Tenacity: Brittle; Fluorescence: Generally none.
Optical Properties
Opaque; Refractive Index: approx 1.54-1.55 (aggregate); No pleochroism or dispersion visible due to opacity and aggregate structure.
Hardness & Durability
Origin Region
Worldwide distribution; commonly found in riverbeds, glacial tills, and sedimentary basins such as the Grand Canyon (USA) or the Chalk formations of Europe.
Hardness & Durability
Mohs Hardness: 6.5 to 7. Very durable and resistant to weathering; high toughness making it ideal for ancient stone tools.
Care & Maintenance
Hardy and stable. Can be cleaned with warm soapy water and a soft brush. Resistant to most household chemicals but can be scratched by harder gemstones like Topaz or Sapphire.
Rarity & Value
Very Common. Low commercial value as a gemstone; primarily valued as a geological specimen or for use in lapidary 'tumbling' and landscaping.
Special Characteristics
Sedimentary banding (rhythmite-like layers) which represents different pulses of mineral deposition or varying impurity concentrations during formation.
Lore & History
Historically used by prehistoric cultures for 'knapping' into arrowheads and tools due to its predictable conchoidal fracture. In modern folklore, banded stones are often called 'earth stones' and are associated with grounding and stability.