sedimentary
Quartz Geode (partially filled/solid)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: White to translucent grey with brown iron oxide/clay staining, Luster: Vitreous to dull (outer), Crystal Structure: Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: White to translucent grey with brown iron oxide/clay staining, Luster: Vitreous to dull (outer), Crystal Structure: Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed by mineral-rich groundwater precipitating silica inside a cavity in sedimentary rock (like limestone) or volcanic gas bubbles. Often found in Mississippian or Ordovician aged strata.
Uses & applications
Used primarily as decorative items, lapidary specimens, educational tools for children, and in metaphysical collecting.
Geological facts
This specimen appears to be a 'solid geode' or nodule, where the silica has completely filled the central cavity, often forming a mass of chalcedony or microcrystalline quartz.
Field identification & locations
Identify in the field by looking for rounded, knobby stones that feel lighter than they look (if hollow) or much harder than the surrounding limestone. Common in Keokuk regions of USA.
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