hercynite


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hercynite

(ˈhɜːsɪˌnaɪt)
n
(Geological Science) mineralogy a black, opaque mineral of the spinel series
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References in periodicals archive ?
It is an oxide mineral belonging to with magnesiochromite (MgCr O ); substitution of aluminum occurs leading to hercynite (FeAl O ).2 4
Careful examination may reveal more occurrences of diopside, but I recall only small subhedral to anhedral grains of what appears to be diopside associated with small hercynite octahedrons and clintonite rosettes near the summit.
The occurrence of orthopyroxene and hercynite, and specific chemical composition of high-grade phases, such as a high Ti content in biotite and a high Al content in orthopyroxene, are in accordance with the other geothermobarometric estimates, which suggests the peak temperature of formation over 800[degrees]C and pressure of 5-6 kbar (Fig.
They were usually classified as either pleonast or hercynite; however always exclusively on the basis of visual microscopic evaluation.
The deoxidation products are [Al.sub.2][O.sub.3] and hercynite ([FeO-[Al.sub.2][O.sub.3]).
The most common of these are hercynite (FeO[Al.sub.2][O.sub.3]) and its solid solution series, and magnetite ([Fe.sub.3][O.sub.4]) (Hofmann 1962, 1966, Longworth and Tite 1979, Longworth and Warren 1975, Maggetti et al., 1981).
Associated minerals are: hematite, ilmenite, pseudorutile, magnetite and hercynite.
The composition of larger lobate grains shows their pertinence to titaniferous magnetite with a higher content of ulvospinel molecule ([Fe.sub.2]Ti[O.sub.4]) and low contents of Mn, Mg, Al, thus forming very low proportions of jacobsite, magnesioferrite, and hercynite, respectively, and sometimes V.
In the +90% alumina refractory system, iron oxide can react with the alumina to form a spinel compound FeO*[Al.sub.2][O.sub.3] (hercynite).
For example, aluminum-coated or killed steel used in cast iron melting will result in alumina or alumina complex mineral deposits such as hercynite (iron aluminate), mullite (silica alumina), etc.
PHOTO : CL micrograph of a buildup sample showing anorthite (yellow), corundum (red) and hercynite (black) crystals.