Sharp black octahedral crystals of the iron-rich spinel hercynite
and small grains of what may be diopside have been found loose in the thin alpine soil along the west slope of Green Monster's summit plateau some 40 meters southwest of the clintonite site.
Even though hercynite is a comparatively rare mineral in granulites, not its presence but its form merits a special attention in the case of the rock examined.
Hercynite grains of the symplectite, mostly hundredths of mm in site, are isometric and almost xenoblastic.
The EMPA data for the spinelid have shown a composition corresponding to hercynite.
An additional x-ray diffraction spectrum showed minor peaks due to hercynite, FeO[Al.sub.2][O.sub.3].
Rather it was more likely due to a metal oxide system as that of iron, possibly including other spinels such as hercynite, in which the changes between the various coloring agents (for example, red hematite contrasted with black magnetite, or maghemite, or wustite, or some combination thereof) are reversible.
FeO + [Al.sub.2][O.sub.3] [approaches] FeO*[Al.sub.2][O.sub.3] hercynite
In spinel-forming refractories that are alumina-enriched, it is possible to form either hercynite or galaxite [ILLUSTRATION FOR FIGURE 3 OMITTED].
Penetration of FeO resulted in formation of hercynite (FeO*[Al.sub.2][O.sub.3]) as determined by x-ray diffraction (XRD).
it often provides the other oxide partner in mineral complexes, such as magnesia/alumina spinel, calcium aluminate, iron alumina spinel (hercynite) and zinc alumina spinel (gahnite).
As a result, the mid-coil ring deposit of iron aluminate (hercynite) leads to ineffective charging and superheat of the lower circulation pattern in about four hours, threatening the integrity of the silica lining.