Flint (variety of Chert)
Quartz (Microcrystalline variety) var. Flint · Mineral Specimen / Industrial Mineral / Decorative Stone
Crystal System
Trigonal crystal system, often occurring in massive, nodular, or tuberous habits with a microcrystalline/cryptocrystalline structure
Mineral Group
Silicates; Tectosilicate (Quartz group)
Chemical Formula
SiO2 (Silicon Dioxide) with trace inclusions of iron oxides (Hearthy/Brown colors) and carbonate remnants
Formation Process
Sedimentary/Diagenetic; formed by the chemical replacement of calcium carbonate by silica-rich fluids in marine environments, often around organic nuclei
About This Crystal
Opaque to translucent nodule with a waxy to dull luster. This specimen shows a weathered 'cortex' (outer skin) with brownish-orange iron staining and distinct white, calcified fossil inclusions on the surface. The interior, visible in chipped areas, is dark gray to tan with a smooth, vitreous to waxy texture.
Physical Characteristics
Color: Brown, tan, and gray with white patches; Streak: White; Cleavage: None; Fracture: Perfect conchoidal (shell-like) with sharp edges; Specific Gravity: 2.6 – 2.65; Fluorescence: Usually inert but can show weak green or yellow under UV if chalcedonic.
Optical Properties
Refractive Index: 1.544 – 1.553; Birefringence: Weak (0.009); Pleochroism: None; Transparency: Opaque to translucent on thin edges; Only weakly doubly refractive due to microcrystalline aggregate nature.
Hardness & Durability
Origin Region
Common in chalk and limestone formations globally, notably from the Chalk Group in Western Europe (UK, France, Denmark) and North America
Hardness & Durability
Mohs Hardness: 6.5 – 7; Toughness: Very High (extremely resistant to breaking, though brittle once a fracture starts); Stability: High, resistant to most acids except Hydrofluoric.
Care & Maintenance
Clean with warm soapy water. Stable under sunlight. Avoid impact as it fractures into extremely sharp, razor-like edges. Store separately from softer stones or jewelry to prevent scratching.
Rarity & Value
Common; Value is generally low for raw specimens, though value increases for worked artifacts (arrowheads) or highly banded 'striped' varieties. Treatments are rare, though heat is sometimes used to improve knapping quality.
Special Characteristics
Displays prominent conchoidal fracture scars and contains fossilized marine remnants (likely bryozoans or shell fragments) visible as white crusts on the surface. Known for creating sparks when struck against steel.
Lore & History
Historically the most important mineral for human evolution, used since the Stone Age for tools and fire-starting. Symbolically associated with protection, grounding, and 'cutting through' obstacles. In traditional practices, it is believed to provide a shield against negativity.