Went to Antreeville today. Despite digging a good bit, my best find was all the way back on the left side of the dump piles. It was laying on the ground & very clean. But you didn't know it had a large crystal in the center of the pocket, unless you picked it up. Lucky for me I did!www.varockhounder.com/uploads/2011042317407455.jpg[/img]
I hate to belittle the subject, but by no stretch of the imagination could that be called a "geode", unless you all want to start "slang" or "pet" names for the vugs from DH.
To clarify; I do not doubt that crystal lined cavities that would satisfy the criteria of the definition of "geode" exist at DH. But they would be rare. Do we really want to create the existence of "geodes" at Diamond Hill?
Last Edit: Apr 24, 2011 8:32:38 GMT -5 by arappaho
Geodes: (Greek γεώδης - ge-ōdēs, "earthlike") are geological rock formations which occur in sedimentary and certain volcanic rocks. Geodes are essentially rock cavities or vugs with internal crystal formations or concentric banding. The exterior of the most common geodes is generally limestone or a related rock, while the interior contains quartz crystals and/or chalcedony deposits. Other geodes are completely filled with crystal, being solid all the way through. These types of geodes are called nodules.
Formation: Geodes can form in any cavity, but the term is usually reserved for more or less rounded formations in igneous and sedimentary rocks, while the more general term "vug" is applied to cavities in fissures and veins. They can form in gas bubbles in igneous rocks, such as vesicles in basaltic lavas, or as in the American Midwest, rounded cavities in sedimentary formations. After rock around the cavity hardens, dissolved silicates and/or carbonates are deposited on the inside surface. Over time, this slow feed of mineral constituents from groundwater or hydrothermal solutions allows crystals to form inside the hollow chamber. Bedrock containing geodes eventually weathers and decomposes, leaving them present at the surface if they are composed of resistant material such as quartz.
Coloration: Most geodes contain clear quartz crystals, while others have purple amethyst crystals. Still others can have agate, chalcedony, or jasper banding or crystals such as calcite, dolomite, celestite, etc. There is no easy way of telling what the inside of a geode holds until it is cut open or broken apart. However, geodes from any one locality usually have a more restricted variety of interior mineralization.
Good summation there, Bryan, thank you. It was great seeing you two at Glendon yesterday, btw.
Thanks, Rick, I needed that. Using that definition, I wonder how many would accept geode as a proper name for this specimen? Personally, I could never call this anything but a crystal-lined cavity. But if that's all it takes to be a geode, so be it. I've got fluorite to clean.