The dark-appearing veins following fractures in the Gold Sheen sapphires appear to have formed after the
exsolution of Fe-Ti oxides.
%) associated with decreasing temperature, so 200 bars (20 MPa) is a reasonable minimum estimate for [H.sub.2]O
exsolution. The bulk density of the crystallized magma is calculated as 2.5 g/[cm.sup.3].
The galena can contain up to 20% Ag (by weight) and in certain circumstances the gold may also be present as replacement or
exsolution blebs in arsenopyrite or pyrite.
There is no kinetic barrier to heterogeneous nucleation of bubbles; therefore, the
exsolution surface (level in the chamber or conduit) is synonymous with the saturation surface because volatiles exsolve during magma ascent (Fig.
The mineral is white and occurs generally interstitial to microcline and quartz, as an
exsolution product within microcline crystals, and in irregular masses as much as 30 cm in maximum dimension.
The chalcopyrite commonly occurs within sphalerite as
exsolution (Figure 4(h)).
The miscibility gap is narrower at high temperatures, so that under slow cooling conditions, early formed augites and low-Ca pyroxenes develop
exsolution lamellae as low-Ca pyroxene and augite (respectively) are expelled from the structures.
Occurrence: The grains in Indarch probably formed by
exsolution of Si and N from kamacite, perryite and schreibersite during parent-body metamorphism.
The primary ore textures comprise euhedral-anhedral-grained, metasomatic, edge-shared, void-filling, poikilitic, slaty cleavage, skeletal,
exsolution, graphic, crumpled, and cataclastic textures (Figure 4).
In ore from Kipushi, needles and grains of gallite occur in sphalerite and in chalcopyrite as
exsolution structures.
Magnetite commonly exhibits an
exsolution texture comprised of intergrown magnetite, hematite, rutile and (rarely) translucent brown euxenite with a yellowish alteration surface.
According to Rodriguez Gallego (1985), structural imperfections in phyllosilicates can be classified into the following groups: 1) point defects; 2) line defects or dislocations; 3) plane defects (polytypism etc.); 4) volume defects (intergrowth,
exsolutions, etc.).
Pyrrhotite occurs as coarse crystals with flame
exsolutions of pentlandite and surrounded by polycrystalline, chain-like pentlandite aggregates, yielding similar textures to those observed in Sudbury ores.
