mineral

Sagenitic Agate (with Goethite/Rutile inclusions)

Silicon Dioxide (SiO2) with hydrous ferric oxide inclusions

Hardness: 6.5-7 (Mohs); Color: Translucent grey to white with brown/black needle-like inclusions; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.58-2.64.

Hardness: 6
Luster: Vitreous to waxy

Identified March 30, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous host rocks (typically basalt). The 'sagenitic' inclusions represent acicular minerals like goethite or rutile that were encased by the silica as it solidified.

Uses & applications

Primarily used for lapidary work, cabochons for jewelry, and as display specimens for collectors who appreciate 'landscape' or 'plume' inclusions.

Geological facts

The term 'sagenitic' comes from the Greek word for 'net'. While often called 'hair stone', these specimens are prized by geologists because the inclusions often preserve the delicate structure of minerals that would otherwise have weathered away.

Field identification & locations

Identify in the field by checking for the translucent, chalcedony-like base and characteristic needle-like or hair-like patterns inside. Common in volcanic regions of Oregon (USA), Brazil, and India. Collectors look for high transparency in the host agate to better see the internal inclusions.

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