Chert / Flint
Quartz (Variety: Chert or Flint) · Mineral Specimen / Sedimentary Rock
Crystal System
Trigonal/Hexagonal; microcrystalline/cryptocrystalline (no visible crystals)
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 (Silicon Dioxide) with impurities of organic matter or iron oxide
Formation Process
Sedimentary; typically forms as nodules in limestone/chalk through the diagetic replacement of carbonate minerals by silica-rich fluids
About This Crystal
Opaque to slightly translucent at edges, gray to black in color with a dull to waxy luster. The specimen shows characteristic conchoidal fracture and a mottled, smooth texture typical of cryptocrystalline silica.
Physical Characteristics
Color: Dark gray/black; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like); Specific Gravity: 2.58–2.64; Tenacity: Brittle; Fluorescence: Generally none.
Optical Properties
Refractive Index: 1.544–1.553; Opaque (light cannot pass through the body of the stone); Non-pleochroic; Singly refractive in micro-clusters.
Hardness & Durability
Origin Region
Globally distributed; UK (Dover), USA (Ohio Flint Ridge), Denmark; found in limestone or chalk beds
Hardness & Durability
Mohs Hardness: 7; Very tough and durable; Resistant to chemicals and weathering; Excellent stability.
Care & Maintenance
Wash with warm soapy water and a soft brush; extremely stable; can handle sunlight and most chemicals, but keep away from impact to avoid chipping sharp edges.
Rarity & Value
Common; low monetary value as a raw specimen; value increases slightly if worked into tools (arrowheads) or polished. Rarely treated.
Special Characteristics
Displays sharp, glass-like conchoidal fracturing; when struck against steel, it produces sparks due to the friction reacting with the silica, hence the name 'Flint.'
Lore & History
Historically critical for human evolution as the primary material for stone age tools and fire-starting. Traditionally associated with protection and grounding; used by ancient cultures for cutting tools and weapons.