Flint
Quartz var. Flint (Chert) · Mineral Specimen / Sedimentary Stone
Crystal System
Trigonal, massive or microcrystalline habit (cryptocrystalline)
Mineral Group
Silicates (Subgroup: Tectosilicates)
Chemical Formula
SiO2
Formation Process
Sedimentary formation, typically occurring as nodules in marine limestone or chalk through the replacement of calcium carbonate by silica-rich solutions in low-temperature environments.
About This Crystal
An opaque, dark grey to black nodular specimen with a characteristic chalky white outer cortex. It exhibits a smooth, waxy to dull luster on the fractured surfaces and a conchoidal fracture pattern.
Physical Characteristics
Color ranges from dark grey/black to brown with a white cortex; streak is white; cleavage is none; fracture is distinctly conchoidal; specific gravity is approximately 2.60 to 2.65; brittle tenacity; lacks magnetism.
Optical Properties
Singly or doubly refractive depending on microcrystalline orientation (aggregate birefringence); refractive index is around 1.544-1.553; non-pleochroic; displays no notable optical phenomena like chatoyancy or asterism.
Hardness & Durability
Origin Region
Found worldwide, prominently in chalk formations in England (such as the Cliffs of Dover), France, and the Midwestern United States.
Hardness & Durability
Mohs hardness of 7; high toughness due to microcrystalline interlocking structure; stable against most chemicals except hydrofluoric acid; excellent durability for wear or striking to create sparks.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid harsh acids; store separately from softer stones to prevent scratching; completely stable in sunlight and standard temperatures.
Rarity & Value
Common; value is generally low and primarily determined by its historical use as a toolmaking material or as a mineral specimen rather than gemological worth; no common treatments.
Special Characteristics
Notable for its extreme conchoidal fracture, which allows it to be easily knapped into sharp edges for ancient tools, and its ability to produce sparks when struck against steel due to localized friction and heat.
Lore & History
Historically significant as one of the primary materials used by early humans for creating stone tools, arrowheads, and fire starters during the Stone Age. In metaphysical practices, it is often associated with grounding, protection, and cutting away energetic blockages.