A stunning garnetResembling something designed and built by the BORG collective, the piece in questi
A stunning garnetResembling something designed and built by the BORG collective, the piece in question is a Spessartine/ite garnet from Brasil that has been etched by caustic fluids at some point in its geological history, probably by partial dissolution when the granite that parented it was slowly cooling and stewing in its own juices. Named after the town of Spessart in Germany that was the original type location they vary from orangey yellow (mandarin or malaya garnet) to red. Spessartine forms a solid solution series with other red garnets, with the mantle sourced pyrope garnets (along with chrome diopside a diamond indicator mineral that erupts in the same kimberlite that carries the diamonds up from the mantle), the mostly metamorphic iron Almandine garnets and these that form mostly in Earth distilled granitic rocks. Garnets in a rock are used as both geobarometers and geothermometers to gauge the ambient temperature and pressure conditions in which the rock formed, and hence the volcanic or metamorphic event.The colour is caused by manganese, and it can also be recognised by its inclusions in a hand lens, which consist of veil patterns of fluid and crystalline inclusions. Major sources include the Umba valley in Tanzania and Kenya (also famous for corundums), Nigeria and Namibia. Colours are natural as these gems are not treated. This crystal is a floater that grew without contact with the walls of the pocket, measures 7.5 x 6.5 x 3 cm and weighs around 215 grams.LozImage credit: Rob Lavinsky/iRocks.com -- source link
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