Chert (Jasper/Flint variety)
Microcrystalline Quartz · Mineral Specimen / Decorative Stone / Semi-Precious (when colorful/patterned)
Crystal System
Trigonal/Hexagonal; Cryptocrystalline (crystals are too small to be seen without a microscope), typically found in massive or nodular habits.
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 (Silicon Dioxide) with impurities of iron oxide (Fe2O3) and clay minerals
Formation Process
Sedimentary/Biogenic or Hydrothermal; forms through the accumulation of silica-rich organic remains (radiolarites/diatoms) or by chemical precipitation of silica from groundwater replacing organic material or filling cavities.
About This Crystal
The specimen is a dense, opaque nodule with a waxy to dull luster. It displays a mottled 'earthy' color palette of brown, tan, and reddish-pink. The surface shows smooth, rounded edges and some planar faces indicating conchoidal fracturing.
Physical Characteristics
Color: Brown, tan, and reddish; Streak: White; Cleavage: None; Fracture: Conchoidal to splintery; Specific Gravity: 2.6-2.65; Tenacity: Brittle; Fluorescence: Generally none.
Optical Properties
Refractive Index: 1.544-1.553; Birefringence: Low (hard to observe in massive form); Opaque; No pleochroism or dispersion effects.
Hardness & Durability
Origin Region
Worldwide; commonly found in sedimentary rock formations (limestone/chalk), riverbeds, and glacial till. Specific regions include Brazil, India, and the Midwestern United States.
Hardness & Durability
Mohs Hardness: 6.5 to 7; Very durable and resistant to weathering, though it can chip or shatter (conchoidal fracture) upon impact.
Care & Maintenance
Safe to clean with warm soapy water and a soft brush. Resistant to most household chemicals but can be scratched by harder stones like topaz or sapphire. Avoid mechanical impact.
Rarity & Value
Common; Value is generally low for rough specimens, though pieces with high iron content (Jasper) or specific colors are valued by lapidaries and collectors.
Special Characteristics
Conchoidal fracture pattern (creating sharp edges), microcrystalline structure, and potentially minor iron-staining (limonite/hematite) causing the red and brown hues.
Lore & History
Historical Significance: Used by prehistoric humans to create tools and weapons (arrowheads, scrapers) due to its sharp edges. Lore: Believed in various cultures to be a stone of protection and grounding, often associated with the Root Chakra.