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Turquoise Jewelry Care
Turquoise has a lower-than-ideal hardness and durability for use in certain types of jewelry. Although the gem is frequently used in rings, bracelets, and belt buckles, these uses place the gem at risk for abrasion and impact. Smart jewelry design will surround the gem with a durable bezel that protects the sides of the gem…
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Turquoise Colors
Blue minerals are rare, and that is why turquoise captures attention in the gemstone market. The most desirable color of turquoise is a sky blue or robin’s-egg blue. Some people inappropriately describe the color as “Persian blue” after the famous high-quality material mined in the area that is now known as Iran. Using a geographic name…
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What is Turquoise?
Turquoise is an opaque mineral that occurs in beautiful shades of blue, bluish green, green, and yellowish green. It has been treasured as a gemstone for thousands of years. Isolated from one another, the ancient people of Africa, Asia, South America and North America independently made turquoise one of their preferred materials for producing gemstones, inlay, and small sculptures. Chemically, turquoise is a hydrous phosphate of…
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The World’s Largest Geode?
Geology.com has numerous articles about Earth Science World Records. These feature the world’s tallest tsunami, world’s largest volcano, world’s tallest geyser and more. We have learned from these articles that picking the largest, tallest, deepest, etc. will be met with disagreements about measurement methods, qualifying criteria, and more. Similar problems surround naming “the world’s largest geode”. The definition of a…
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Amethyst Amygdules of Brazil and Uruguay
Without question, the most spectacular geode deposit ever discovered is the amethyst amygdule basalts of Rio Grande do Sul region of Brazil and adjacent Uruguay. About 160 million years ago, when plate tectonic processes were rifting Africa and South America apart as the Atlantic Ocean opened, one of the world’s great flood basalt events was…
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Other Famous Geode Localities
There are hundreds of areas around the world where geodes of various types can be found in abundance. Most of these deposits are small and support the collecting activities of a few rockhounds. However, other deposits are extensive, with enough geodes to support a commercial collection and manufacturing industry. Oco (Ocho) Geodes Oco or Ocho…
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Oregon Thundereggs
Thundereggs are not geodes, but they are so similar that they deserve at least one locality mention in this article. The state of Oregon is the most famous thunderegg locality in the world. Thundereggs are found in rhyolite and tuff deposits in many parts of the state. In 1965 the Oregon Legislative Assembly issued a…
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Arizona Gem Silica Geodes
Some unusual geodes and nodules found at the Inspiration Mine in Gila County, Arizona are lined with gem silica, a rare, beautiful and valuable form of blue chalcedony. Some have been found with gem silica stalactites!
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Woodbury Geodes
Woodbury geodes occur in the area around Woodbury, Tennessee. They originated in the limestones and dolostones of the Warsaw Formation and can be seen where these rock units are outcropping. Liberated geodes are found in residual soils above the rock units in which they formed, and in the sediments of the valleys that drain these…
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Geodes of Indiana
In south-central Indiana geodes can often be seen in exposures of the Harrodsburg Limestone and Ramp Creek Formations. The Indiana Geological Survey reports that geodes are abundant along streams and scattered on the ground for several miles on either side of their outcrop areas.