sedimentary
Chert (Field Stone)
Microcrystalline Quartz (SiO2)
Hardness 7.0 Mohs; Dull to waxy luster; Conchoidal fracture; Grey to brownish-tan color; Cryptocrystalline structure; High density.
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Physical properties
Hardness 7.0 Mohs; Dull to waxy luster; Conchoidal fracture; Grey to brownish-tan color; Cryptocrystalline structure; High density.
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation within sedimentary layers, often millions of years old.
Uses & applications
Historically used for making stone tools (arrowheads); currently used as construction aggregate or road base.
Geological facts
Chert comes in many varieties including jasper, flint, and agate; it is chemically stable and resistant to weathering.
Field identification & locations
Identify by its hardness (it will scratch steel) and its shell-like fracture pattern. Often found in riverbeds or within limestone outcrops.
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