Chert (variety of Quartz)
Silicon Dioxide (Microcrystalline Quartz) · Mineral Specimen / Sedimentary Rock Component
Crystal System
Trigonal (specifically microcrystalline or cryptocrystalline), typically occurring in massive, nodular, or bedded habits.
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2
Formation Process
Sedimentary/Diagenetic. Typically forms through the accumulation of siliceous oozes or the replacement of carbonate minerals by silica-rich groundwater.
About This Crystal
The specimen shows a dense, fine-grained texture with a dull to waxy luster. Color is predominantly grey to brownish-grey with significant weathering crust (patina). It is opaque with an earthy surface and evidence of conchoidal fracture patterns.
Physical Characteristics
Color: Grey, tan, brown; Streak: White; Cleavage: None; Fracture: Conchoidal to splintery; Specific Gravity: 2.6 – 2.65; Fluorescence: Generally none, occasionally inert/dull green.
Optical Properties
Isotropic/Microcrystalline. Refractive Index: ~1.54. No visible pleochroism or dispersion due to its opaque, aggregate nature.
Hardness & Durability
Origin Region
Found globally; notable deposits in the United States, UK (as Flint), and Jordan. Common in marine limestone and chalk formations.
Hardness & Durability
Mohs Hardness: 6.5 – 7. Very tough and durable due to its lack of cleavage and intertwined microcrystalline structure.
Care & Maintenance
Hardy material; can be cleaned with warm soapy water and a soft brush. Resistant to most household chemicals but should be kept away from hydrofluoric acid.
Rarity & Value
Very Common. Primarily used for industrial purposes or as a geological specimen. Value is generally low unless it contains unique fossils or high-color Jasper-like patterning.
Special Characteristics
Displays classic conchoidal (shell-like) fracturing which produces sharp edges. May contain micro-fossils or organic inclusions.
Lore & History
Historically vital for human development; used to create stone tools, arrowheads, and fire-starters (flint). Culturally associated with protection and grounding in various folk traditions.