sedimentary

Chert (Chalcedony/Agate)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, and cream; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.65

Hardness: 6
Color: Brown, tan, and cream
Luster: Waxy to vitreous

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and cream; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater or within sedimentary rock layers like limestone. Found in the Saharan regions of Sudan where ancient volcanic activity and subsequent silification occurred.

Uses & applications

Historically used for stone tools and arrowheads; currently used as semi-precious gemstones, in decorative lapidary work, and for landscaping.

Geological facts

This region of northern Sudan (Bayuda Desert/Nubian Desert) is rich in Neolithic stone artifacts made from similar materials due to its hardness and ability to hold a sharp edge.

Field identification & locations

Identified by its waxy luster, smoothness, and conchoidal (shell-like) fracture. Commonly found as river pebbles or desert lag in ancient drainage basins.