sedimentary

Agatized Fossil or Chalcedony Nodule

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5-7 (Mohs scale); Color: Cream, tan, grey with translucent patches; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic fibers); Cleavage: None/Conchoidal fracture; Specific gravity: 2.58-2.64

Hardness: 6
Color: Cream, tan, grey with translucent patches
Luster: Waxy to vitreous

Identified May 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica-rich fluids within cavities of sedimentary host rocks or by replacing organic material (silicification) over millions of years, typically during the Cenozoic or Mesozoic eras.

Uses & applications

Commonly used for lapidary work (polishing, cabochons), decorative display specimens, and as a durable material for stone tools in prehistoric times.

Geological facts

This specimen appears to be water-worn, likely found in a riverbed or coastal area. The waxy surface and translucent spots are classic indicators of chalcedony, a microcrystalline form of quartz.

Field identification & locations

Identify in the field by checking for translucency (light-bleeding) when held to a torch, a waxy feel, and a heavy weight for its size. Often found in gravel beds or areas with volcanic or limestone history.

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