File:Blueschist with benitoite-neptunite-natrolite vein (Franciscan Complex, Jurassic-Cretaceous; Middle Miocene vein mineralization, 12 Ma; Dallas Gem Mine, California, USA) 2 (32832839407).jpg
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Benitoite crystals from California, USA. Blue = benitoite White = natrolite Black sticks = neptunite Host rock = blueschist The bluish-colored crystals shown above are benitoite, a very rare barium titanium silicate mineral (BaTiSi3O9) known principally from San Benito County, California, USA. Large, gem-quality crystals that have been cut, faceted, and polished have the “fire” of diamond (~same index of refraction), but have a lovely deep blue color (<a href="http://www.jewelryexpert.com/catalog/graphics/Fancy-Trillium-Benitoite-1.gif" rel="noreferrer nofollow">www.jewelryexpert.com/catalog/graphics/Fancy-Trillium-Ben...</a>). Benitoite is a metamorphic mineral. Its principal occurrence is in California, where polymineralic veins have intruded a blueschist body between serpentinites and greenstones of the Franciscan Formation. The Franciscan Fm. is a widespread, heterolithic unit of Jurassic-Cretaceous age in the Coast Ranges of western California. The vein mineralization age is late Middle Miocene (12 Ma). Four minerals are commonly found in these veins: benitoite (blue), neptunite (blackish - Na2KLi(Fe,Mn)2Ti2Si8O24), natrolite (white - Na2Al2Si3O10·2H2O), and joaquinite (orangish-brown - Ba2NaCe2FeTi2Si8O26(OH,F)·H2O). The natrolite portion is acid-soluble. Nicely crystalline rock faces like the one shown above are produced by acid etching the natrolite-dominated veins. After acid treatment, the other minerals stand out in relief. Stratigraphy of blueschist host rock: Franciscan Complex, Jurassic-Cretaceous Age of benitoite-bearing vein mineralization: Middle Miocene, 12 Ma Locality: Dallas Gem Mine (a.k.a. Benitoite Gem Mine), near Santa Rita peak, southeast of New Idria, far-southeastern San Benito County, California, USA (~36° 20’ 10” North latitude, ~120° 36’ 19” West longitude) |
| Date | |
| Source | Blueschist with benitoite-neptunite-natrolite vein (Franciscan Complex, Jurassic-Cretaceous; Middle Miocene vein mineralization, 12 Ma; Dallas Gem Mine, California, USA) 2 |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/32832839407 (archive). It was reviewed on 4 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 14:52, 4 November 2019 | | 2,482 × 3,278 (5.26 MB) | Ainz Ooal Gown (talk | contribs) | Transferred from Flickr via #flickr2commons |
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