My father-in-law at Jewelry by CnC researches and collects some of the most unusual, unique and awesome mineral and rock specimens. Here is one that he found at Tucson a few years back and is now hitting the market at incredible prices, due mostly in part because it difficult to get and also for its unusual form and uniqueness.A very unusual form of Agate comes from Minas Gerais, Brazil. It is known as a Polyhedral Agate and is formed by silica replacing the normal calcite resulting in a highly angular form within the rocks instead of the usual sub-spherical forms as normally seen.
These polyhedral quartz pseudomorphs without calcite were mined during the 1970’s and have since then become increasingly uncommon in today's market, with most examples appearing as thin slabs, normally polished front and back to show off the natural beauty of the agate. It's sharp polyhedral form is entirely natural in origin.
Many of the beautiful Agates coming from Minas Gerais today, like the one seen here to the right, will have some slightly pointed sections to their designs, indicating that there is still some silica within the calcite in the Agate itself.
Collectors scramble to obtain samples of a Polyhedral Agate, especially one that still is made up of most of the rock as in this example to the right from an upcoming Australian mineral auction.
Thanks to Lee at Jewelry by CnC for the research and pictures.
