mineral
Quartz Geode (partially opened)
Silicon Dioxide (SiO2) with iron staining
Hardness: 7 (Mohs); Color: White, tan, brown (due to iron); Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- White, tan, brown (due to iron)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs); Color: White, tan, brown (due to iron); Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.65
Formation & geological history
Formed as secondary mineral precipitates in hollow vesicles (voids) of volcanic rock or in sedimentary pockets. The outer shell is often chalcedonic with an inner druse of quartz crystals.
Uses & applications
Primarily used for hobbyist collecting, teaching geology, and as decorative pieces or jewelry (when sliced).
Geological facts
Geodes are known as 'surprise rocks' because their exterior looks like an ordinary round stone, but the interior can contain spectacular crystal formations. The name comes from the Greek word 'Geoides' meaning earth-like.
Field identification & locations
Identify in the field by their rounded, lumpy appearance and their lighter weight compared to solid rocks. Often found in dry desert environments, limestone beds, or areas with ancient volcanic activity.
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