sedimentary

Chert (Pink Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Opaque shades of pink, tan, and reddish-brown. Luster: Waxy to dull. Crystal Structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6 - 2.65.

Hardness: 6
Color: Opaque shades of pink, tan, and reddish-brown
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater within limestone or chalk beds. Often Paleozoic to Mesozoic in age.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges. Modernly used as road aggregate, in landscaping, and sometimes for lapidary work (cabochons).

Geological facts

Because it breaks with a conchoidal fracture, it was the primary material for 'knapping' arrowheads and spear points by prehistoric humans. Pink varieties are often colored by trace amounts of iron oxide (hematite).

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules or layers in limestone formations globally, with notable deposits in the central United States (e.g., Missouri, Arkansas).

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Brecciated Chert (Microcrystalline Silica)

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