sedimentary
Druzy Quartz Geode (Partially Open)
Silicon Dioxide (SiO2) within Sedimentary Host Rock
Hardness: 7 on Mohs scale; Color: Clear to white crystals in a grayish/brown matrix; Luster: Vitreous (glassy) crystals with earthy matrix; Crystal Structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Clear to white crystals in a grayish/brown matrix
- Luster
- Vitreous (glassy) crystals with earthy matrix
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Physical properties
Hardness: 7 on Mohs scale; Color: Clear to white crystals in a grayish/brown matrix; Luster: Vitreous (glassy) crystals with earthy matrix; Crystal Structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: 2.65.
Formation & geological history
Formed when mineral-rich groundwater percolates through cavities in sedimentary or volcanic rock. Over thousands of years, silica precipitates out of the water to form layers of chalcedony and eventually crystalline quartz. These particular specimens are common in limestone or shale beds from the Paleozoic or Mesozoic eras.
Uses & applications
Commonly used for home decor, educational material in geology, and minor jewelry (when cut into druzy cabs). Lapidary artists use them for polishing or as display pieces.
Geological facts
Geodes are virtually indistinguishable from ordinary rocks on the outside until cracked open. The word 'geode' comes from the Greek word 'Geoides,' meaning 'earth-like.' These specimens often represent a micro-environment that has remained sealed for millions of years.
Field identification & locations
Identify in the field by looking for rounded, bumpy, or hollow-sounding nodules that feel lighter than solid rocks of the same size. Common locations include the Midwest USA (Keokuk geodes), Brazil, and Morocco. Collectors should look for well-defined crystal terminations and lack of damage.
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