andradite


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andradite

[an′drä‚dīt]
(mineralogy)
The calcium-iron end member of the garnet group.
References in periodicals archive ?
Finger, "High-pressure crystal chemistry of andradite and pyrope: revised procedures for high-pressure diffraction experiments," American Mineralogist, vol.
A new deposit of andradite garnet of the demantoid and topazolite varieties has recently been discovered in Antetezambato, Ambanja area, Antsiranana province, North Madagascar.
Lacroix (1922) described garnet occurrences in Madagascar, especially andradite in igneous rocks, and reported the discovery of some crystals of pale green andradite lining cavities in a nepheline-bearing syenite at Mount Bezavona.
Takeda include some fine specimens of dark red-brown vesuvianite found three years ago in the old Kobushi mine, Nagano Prefecture, with sleek, lustrous tetragonal-prismatic crystals to 5 cm long; a couple of excellent thumbnails of axinite-(Fe) from the Obira mine, Oita Prefecture (another old classic); and plenty of good small specimens of "rainbow" andradite from Kitakado, henmilite from the Fuka mine, and crystallized native arsenic from the Akatani mine.
Andradite [Ca.sub.3][Fe.sub.2.sup.3+][([SiO.sub.4]).sub.3]
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.
In Munich, Laurent Gautron of 3G Environnement (3genvt@wanadoo.fr) had perfect, sharp, lustrous, loose dodecahedral crystals of "grandite" (as some have nicknamed the compositionally zoned mixture of grossular and andradite) reaching 5 cm in diameter, including some complexly mottled yellow-brown crystals, and including also a few of the odd "window" specimens that appear rarely on the market.
(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).
Jeff also showed me the only other new thing he had seen that I had not seen: a new find of andradite garnet in superb apple-green crystals collected very recently at the Black Lake mine, Lac D'Amiante, Thetford, Quebec (these also appeared at the Tucson Show: see that show report in the May-June 2007 issue).
Among the skarn silicates, andradite is the best crystallized, occurring as colorless to greenish brown and dark brown crystals to 1 cm which display {110} and/or {211} forms.
For exciting examples, see below under California and Venezuela gold; California ferro-axinite; Thetford Mines, Quebec andradite; Ojuela mine, Mexico mimetite and hemimorphite; Peruvian rhodonite; Madagascar liddicoatite; Kazakhstan copper; Pakistan anatase and brookite; and many more.
Outcrop collecting sites in the Seriphos skarn rocks are well known for producing fine specimens of ilvaite, andradite and, most of all, the world's best "green quartz," but little has been heard lately of the occurrence.