sedimentary
Chert (specifically Novaculite or Porcelainite)
Microcrystalline to Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, beige, or white with reddish-brown oxidation; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Tan, beige, or white with reddish-brown oxidation
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, beige, or white with reddish-brown oxidation; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone. This specimen shows porcelainous textures typical of high-purity chert or novaculite, often associated with Paleozoic or Mesozoic era formations.
Uses & applications
Historically used for making stone tools (arrowheads/knives) due to sharp edges; currently used as abrasive materials, road ballast, or as oilstones for sharpening blades.
Geological facts
Chert is so durable that it can remain unchanged for millions of years while the surrounding rock erodes away. High-purity novaculite from Arkansas is world-famous for being the finest material for sharpening steel tools.
Field identification & locations
Identify by its waxy texture, extreme hardness (it will scratch glass), and conchoidal (shell-like) fractures. It is commonly found in stream beds or as nodules within limestone outcrops.
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