Agate and Quartz Geode
Image: <a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a> (CC BY 2.0)
Mineral NameAgate and Quartz Geode
Chemical FormulaSiO2
Mohs Hardness7
Crystal Systemtrigonal
Lustervitreous
Streak ColorWhite
CleavageNone
FractureConchoidal
Specific Gravity2.65
Colorsbrown, yellow, gray, white, purple
TransparencyTranslucent to transparent
Type LocalityCleveland Museum of Natural History, Ohio, USA (display location)
Mineral GroupSilicates
Usesjewelry, ornamental, collector
Associated Mineralsagate, quartz, amethyst
Raritycommon
Description
This is a cut slice of a geode, featuring concentric bands of brownish, yellowish, and grayish agate, with a central cavity lined by sparkling white and purple (amethyst) quartz crystals.
Geological Context
Geodes are crystal-lined cavities that form when mineral-rich water enters a void in a host rock, precipitating layers of chalcedony (agate) and then larger quartz crystals over time.
