Douglas Sherman
Staff
Today I'm going to do Geodes. Most people think that geodes only contain quartz crystals but there are a wide variety of crystals that can occur in these objects. Geodes form on the inside of openings in limestone or dolostone. Mineral rich waters can percolate through the rocks and deposit their elements in the openings. The outermost layer of a geode is usually chalcedony, a very dense microcrystalline variety of quartz. You can see it in the images here. Eventually, the crystals of the invading elements grow inward as the chemical composition of the solution changes thus creating the beautiful array of crystals. Amethyst was, at one time, a precious mineral until a bonanza of geodes were found in Brazil lined with these beautiful crystals.
It was possible, in the past, to hunt for geodes at good collecting sites, but like most everything else these sites were put on the internet, and now they are severely picked over.
A geode mostly filled with small calcite crystals from Bloomington, Indiana.
Blue Celestite crystals line this geode from Madagascar.
Mostly quartz crystals with one Calcite Crystal in a Geode from Keokuk, IA
In this specimen you can see the outer chalcedony deposit and the inner amethyst crystals.
It was possible, in the past, to hunt for geodes at good collecting sites, but like most everything else these sites were put on the internet, and now they are severely picked over.
A geode mostly filled with small calcite crystals from Bloomington, Indiana.
Blue Celestite crystals line this geode from Madagascar.
Mostly quartz crystals with one Calcite Crystal in a Geode from Keokuk, IA
In this specimen you can see the outer chalcedony deposit and the inner amethyst crystals.
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