Tiffany Stone
Tiffany stone is a beautiful and rare gem rock, usually opaque, and rarely translucent. Its nature is controversial because, while it can resemble certain agates or jaspers, it is neither. Tiffany stone is a combination of opal, chalcedony, and dolomite in various proportions, infused with colored minerals, most commonly fluorite, in widely varying patterns. Rocks vary in appearance so greatly that it is said that no two are alike. Gem quality tiffany stone is composed mostly of opal and chalcedony, with swirling patterns of colored minerals. Conclusive inclusions of Mt. Laird tuff particles will be small, and may be difficult to detect.
The presence of white, purple, red, orange, black, yellow or green minerals enhance the value and appearance of the rock, but are not a significant factor in identification. Tiffany stone often shows strongly fluorescent patterns under ultraviolet light.
Tiffany stone is found only in one part of the Thomas Mountain Range in western Utah. It was formed first by volcanic action when large bubbles (clasts) were formed in dolomitic lava as it cooled. Then ground water carrying fluorite, silica, and various other minerals filled the cavity with the opal and chalcedony mixture that we know today as tiffany stone. For reasons I do not understand, these minerals were usually deposited in irregular masses instead of the concentric layers associated with agate. The content of the seeping ground water and the pattern of silicification randomly determine the exact pattern to be found in each stone.
Tiffany stone nodules are formed somewhat like geodes, from the outside in, so they sometimes have small cavities in the center that may be lined with tiny silica crystals. Some specimens are structurally weak because they include too many large silica crystals, internal stresses caused by dissimilar mineral inclusions are too great, or other factors. Specimens that contain too much dolomite or show too many hairline cracks will probably not be suitable for cutting.
The presence of white, purple, red, orange, black, yellow or green minerals enhance the value and appearance of the rock, but are not a significant factor in identification. Tiffany stone often shows strongly fluorescent patterns under ultraviolet light.
Tiffany stone is found only in one part of the Thomas Mountain Range in western Utah. It was formed first by volcanic action when large bubbles (clasts) were formed in dolomitic lava as it cooled. Then ground water carrying fluorite, silica, and various other minerals filled the cavity with the opal and chalcedony mixture that we know today as tiffany stone. For reasons I do not understand, these minerals were usually deposited in irregular masses instead of the concentric layers associated with agate. The content of the seeping ground water and the pattern of silicification randomly determine the exact pattern to be found in each stone.
Tiffany stone nodules are formed somewhat like geodes, from the outside in, so they sometimes have small cavities in the center that may be lined with tiny silica crystals. Some specimens are structurally weak because they include too many large silica crystals, internal stresses caused by dissimilar mineral inclusions are too great, or other factors. Specimens that contain too much dolomite or show too many hairline cracks will probably not be suitable for cutting.
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