Moroccan Geode with Quartz Crystals
Geodes are rock and crystalline formations found
in volcanic and sedimentary rock. 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.
A geode begins as a bubble in volcanic rock or
a hollow in sedimentary rock. The outer shell of the bubble or hollow
will eventually harden, and water forms on the inside of the cavity. The
water contains silica precipitation that contains a variety of
These hollows remain full with mineral rich water or get filled again if the water table rises. This water then with the constant drying out then re-depositing of mineral water forms the crystalline structures over a very long period of time. Another way these crystals form is through a leaching process. As the mineral rich ground water permeates the hollow, it begins to form the chalcedony shell through silica deposits. After continual permeation the remaining deposits eventually form hexagoshaped crystals and entirely fill the hollow if allowed to grow. On occasion some geodes that are completely filled have an inner layer of agate surrounded by the hexagon crystals. This is thought caused by a silica gel that got through the chalcedony and later dried.
This Geode comes from Morocco. It measures at: