andradite


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andradite

[an′drä‚dīt]
(mineralogy)
The calcium-iron end member of the garnet group.
References in periodicals archive ?
It was only in November 2008 that French gem dealer Jacque le Quire brought some rough and cut gemstones to the gemological school of the University of Nantes, where they were identified as the andradite variety demantoid (Mocquet et a.
Microprobe analyses and preliminary petrographic observations in thin sections indicate that the microcrystals of garnet constituting the massive rock are zoned, with compositions ranging from intermediate between grossular and andradite to nearly pure andradite.
This intrusion phase activated a high-temperature pneumatolytic to hydrothermal circulation of fluids that was concentrated along rock discontinuities, metasomatically altering the sedimentary rock into a skarn and depositing andradite in cavities.
To establish definitively the age of the Antetezambato lamprophyres and thereby the age of the formation of the andradite crystals, the author is currently conducting isotope-geochronological analyses on selected specimens, the results of which should be available soon.
Non-gem andradite is typically found in skarns, is opaque and is commonly a more or less brownish color.
Opaque brown andradite crystals, most commonly rhombic-dodecahedral, are not uncommon in the mine, but the beautiful, gemmy green trapezohedral crystals of the demantoid variety are extremely rare.
All green andradite crystals from Lac d'Amiante vary in color depending upon the light source (a property called metamerism), appearing pale green to emerald-green in sunlight and under neon lamps, and pale bluish gray-green to bluish green under incandescent and halogen lamps.
After that time, green andradite garnets of good quality have been found only once, in September 2006, when loose crystals to 3 cm were collected, a few of these making it to the 2007 Tucson Show (Moore, 2007).
6-cm group of six sharp, lustrous, emerald-green andradite crystals to 3 cm, joined by a white albite blade; this specimen was brought to the 2007 Sainte Marie-aux-Mines show (Larson, 2007), and a photo of it was published in the same year in Le Regne Mineral (no.
It has also produced (as mentioned) brown opaque andradite garnets, globular prehnite, colorless and transparent apophyllite-(KF), stilbite, stellerite, chabazite-Ca, dark vesuvianite in acicular crystals, zoisite (as the pink variety "thulite"), albite, clinochlore, antigorite, nephrite, chrysotile, rutile, galena, pyrite, magnetite, chromite, diopside, aragonite, fine yellow calcite and quartz (andradite, calcite and quartz are very rare at the famous Jeffrey mine at Asbestos).
2) Ijolite refers to a series of plutonic rocks containing nepheline and 30-60% mafic minerals, generally clinopyroxene, and including titanite, apatite and sometimes andradite (Jackson, 1997).
11 extraordinary specimens from the collection of Irv Brown); native elements (the Mineralogical Association of Dallas); andradite specimens from Alamos, Sonora, Mexico (self-collected by Marty Houhoulis); and a fine small case about Arizona mining history, with old postcards and stock certificates, miners' lamps, Bisbee specimens, etc.