Chert (Commonly known as Flint)
Cryptocrystalline Quartz (Silica) · Mineral Specimen / Industrial Mineral / Decorative Stone
Crystal System
Trigonal crystal system; occurs in microcrystalline or cryptocrystalline massive habit (no visible crystals)
Mineral Group
Silicates (Tectosilicate subgroup)
Chemical Formula
SiO2 (Silicon Dioxide) with possible trace Fe2O3 (Iron Oxide) inclusions
Formation Process
Sedimentary; formed through the chemical precipitation of silica-rich fluids or the replacement of carbonate material in marine environments.
About This Crystal
A dense, hard, cryptocrystalline sedimentary rock. It appears opaque to slightly translucent on thin edges with a dull to sub-vitreous luster. The color is typically grey, tan, or brown with a smooth, waxy surface texture.
Physical Characteristics
Color: Grey and tan; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like) with sharp edges; Specific Gravity: 2.6 – 2.7; Fluorescence: Usually inert but may show weak green or yellow under UV.
Optical Properties
Refractive Index: 1.544 – 1.553; Birefringence: Low to none visible in hand specimen; pleochroism: none. It is an aggregate of microscopic quartz crystals.
Hardness & Durability
Origin Region
Global distribution; commonly found in the United Kingdom (Chalk formations), USA (Ohio Flint Ridge), and Brazil. Occurs in sedimentary limestone or chalk beds.
Hardness & Durability
Mohs Hardness: 6.5 – 7. Highly durable and tough due to its microcrystalline structure; resistant to chemical weathering but brittle enough to produce sharp edges when struck.
Care & Maintenance
Relatively indestructible; can be cleaned with warm soapy water and a soft brush. Resistant to most household chemicals and sunlight, though can chip if dropped due to conchoidal fracture.
Rarity & Value
Common; generally low monetary value unless it is a specific colorful variety like Jasper or high-quality archaeological artifacts. Value is primarily historical or industrial.
Special Characteristics
Produces sparks when struck against steel (flint and steel); exhibits excellent conchoidal fracture, allowing it to be fashioned into sharp tools or arrowheads.
Lore & History
Historically crucial for human development; used in the Stone Age for tools and weapons. Symbolizes grounding and survival. In folklore, it was believed to ward off evil spirits and was used as 'elf-shot' protection.