What a lovely garnetThe beautiful green grossular (calcium rich) garnet known as Tsavorite is only f
What a lovely garnetThe beautiful green grossular (calcium rich) garnet known as Tsavorite is only found in a national park in Kenya, and here is the largest one mined so far. Its hardness (7.5 on Mohs scale) and high lustre rapidly made it popular amongst jewellery buyers after its discovery a couple of decades ago by the same geologist who bought us Tanzanite. . It is usually less included than emerald, and its colour can rival the best beryl can offer. The colour is caused by the same elements within its crystal structure absorbing parts of the white light passing through: Chromium or Vanadium. Unlike emerald it is neither treated to improve its colour or its clarity (emeralds are at least usually oiled or resined to hide and stabilise the cracks). It also is more robust than emerald, as the fractures tend to make the latter brittle.The gems are of metamorphic origin, being born in a episode of mountain building that compressed and heated sedimentary rocks, transforming their constituents into new minerals. Their host rock is a Precambrian graphite schist (the graphite comes from metamorphosed organic material from the original marine sediments). The garnet occurs as shattered porphyroblasts (large metamorphic crystals, often rotated by the pressure of the deep Earth) within the schist.It came from the Merelani Tanzanite mine, some 160 metres down and weighed 180 grams before being (sadly) cut into a step cut gem. Since even a 2 carat Tsavorite is a rarity, the 325 carat cut piece will remain unique unless some other pocket of large crystals makes its appearance.LozImage credit: Multicolourhttp://bit.ly/1Tm58Zk -- source link
Tumblr Blog : the-earth-story.com
#mineral#crystal#garnet#tsavorite#chemistry#chromium#vanadium#schist#metamorphic#precambrian#merelani#tanzanite