Rock Identifier
Botryoidal Chalcedony (likely Desert Rose/Agatized Geode Crust) (Silicon Dioxide (SiO2)) — mineral
mineral

Botryoidal Chalcedony (likely Desert Rose/Agatized Geode Crust)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: White, tan, or grey with a 'cauliflower' or grape-like habit; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (Trigonal); Cleavage: None; Specific Gravity: 2.58-2.64.

Hardness
6
Color
White, tan, or grey with a 'cauliflower' or grape-like habit
Luster
Waxy to dull
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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: White, tan, or grey with a 'cauliflower' or grape-like habit; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (Trigonal); Cleavage: None; Specific Gravity: 2.58-2.64.

Formation & geological history

Formed through the precipitation of silica from low-temperature hydrothermal fluids or groundwater in cavities of volcanic or sedimentary rocks. The 'botryoidal' (bunch of grapes) shape occurs as mineral layers grow around a central nucleus.

Uses & applications

Commonly used for lapidary work (cabochons), as decorative garden stones, in jewelry when dyed or agate-banded, and as popular specimens for mineral collectors.

Geological facts

This specimen displays a distinct botryoidal habit. Often, these are found as the outer crust of geodes or 'desert roses.' The term chalcedony strictly refers to the microcrystalline form of silica which includes agate and jasper.

Field identification & locations

Identify in the field by its rounded, bubble-like surface and its ability to scratch glass (high hardness). Common in arid environments like the American Southwest, Morocco, and Mexico. Collectors look for pieces with minimal bruising and interesting color banding.

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