cronstedtite


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cronstedtite

[′krän‚sted‚īt]
(mineralogy)
Fe42+Fe23+(Fe23+Si2)O10(OH)8 A black to brownish-black mineral consisting of a hydrous iron silicate crystallizing in hexagonal prisms; specific gravity is 3.34-3.35.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Black crystals of cronstedtite with triangular cross-section, displaying only {20[bar.2]1} and {0001} faces, as well as compact masses of cronstedtite, were once found on hisingerite, marcasite, pyrite, siderite and rhodochrosite.
Reddish to brown, gum-like amorphous masses of hisingerite are common at Llallagua, sometimes associated with cronstedtite. Hisingerite can be soft and plastic when first found underground, but rapidly becomes hard and very brittle after removal from the mine.
Both spherical aggregates and thin seams occur on or in a brownish clay matrix containing small grains of pyrite, occasional pyrrhotite and/or minor siderite and black cronstedtite. There are also heavily weathered samples of nikischerite perched on crystals of vivianite, but these samples were found several years ago in a different part of the mine, and were not observed in situ.
Hunanui has also been the source of a number of other fine specimens, available from Alfred, Rock Currier (Jewel Tunnel Imports) and others: large vivianite crystals; superb large (to 4 x 4 cm) parallel groupings of lime green ludlamite crystals on pyrite, siderite, and vivianite matrix; lustrous ferberite V-twins (to 15 x 15 cm) and several specimens (to 7 x 5 cm) of openly branched cronstedtite crystals (to 5 mm) on matrix were also offered.
Saura also had a selection of less common Spanish minerals, including ludlamite crystals to 5 mm (some with associated vivianite crystals) and groups of cronstedtite from the Brunita mine, La Union district.