gahnite


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gahnite

[′gä‚nīt]
(mineralogy)
ZnAl2O4 A usually dark-green, but sometimes yellow, gray, or black spinel mineral consisting of an oxide of zinc and aluminum. Also known as zinc spinel.
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These include: annabergite, aragonite, argentopentlandite (Sirka, 1988), brochantite, chlorite (group), covellite, devilline, erythrite, gadolinite, gahnite, goethite, gold-silver (electrum), illite, kaolinite, langite, malachite, montmorillonite, natrojarosite, naumannite (Frigstad, 1972), palygorskite, posnjakite, scheelite, sepiolite (van der Wel, 1972), stilpnomelane, sulfur, tetrahedrite and tremolite-actinolite.
These anomalies are characterized by sulphide paragneiss with variable amounts of accessory pyrrhotite +/- magnetite +/- garnet +/- biotite +/- gahnite.
Associated minerals are: quartz, magnetite, spessartine-rich garnet, "apatite," sillimanite, ferroan gahnite, sulfides, Mn-rich grunerite (in places manganogrunerite), manganoan fayalite and Mn-rich pyroxferroite.
The type material (Greece) is from an emery and is associated with: corundum (partly altered to diaspore), chloritoid, Ti-rich hematite, ilmenite, gahnite, "tourmaline," rutile, and calcite.
The mineral is stated to occur as epitactic overgrowths on gahnite crystals with [001] of zincohogbomite parallel to [111] of gahnite.
Probe standards are as follows: cobaltite (As); gahnite (Zn); spessartine (Mn); forsterite (Mg); fayalite (Fe); kyanite (Al).
The following standards were used: Cd: Cd metal; Cu: olivenite; As: cobaltite; K: orthoclase; Ca: diopside; Mn: spessartine; Zn: gahnite.
Subhedral green grains and blebs of gahnite in granular sulfides have been identified by EDS and optical analysis (George Robinson, pers.
Additional minerals present include zircon, gahnite, minor spessartine, hectorite and coronadite, and secondary phosphates fluorapatite, eosphorite and crandallite.