3A) as scattered euhedral cubic-octahedral crystallites, framboid
aggregates or bundles (concretions) of framboidal aggregates.
Dean, "History of watercolumn anoxia in the Black Sea indicated by pyrite framboid
size distributions," Earth and Planetary Science Letters, vol.
In modern euxenic environments the mean framboid
diameters are generally smaller (below 10 [micro]m) and have a narrower size range than for oxic and dysoxic environments (Wilkin et al.
The composition of a typical electron opaque coating was determined by elemental analysis on a transect across the framboids
' outer coating, fractured whilst mounting the framboid
on the SEM stub (Fig.
It occurred as isolated framboids
, as elongated clusters of framboids
disseminated in the clay matrix (Figure 4(e)), as replacement/infillings of bioclasts (Figure 4(b)), and as rare pyrite nodules.
Pyrite and other sulfide minerals are often found in shales and carbonate bedrock as small (2-20 pm) framboids
(Schieber, 2011; Smedley & Kinniburgh, 2002, 2005).
Pyrite is common as crystals or small nodules, framboids
or replacement of macrofauna (mainly ammonites).
The mineral matrix pores are mainly developed between and within calcite crystals, quartz grains, clay minerals and pyrite framboids
. The organic matter usually contains pores of several shapes and sizes (micro-meter to nanometer scale), which are sometimes connected by narrow throats.
The presence of what appear to be degraded pyrite framboids
in the deeper horizons of both apicum soils (Fig.
A lump of biological indicators as algae, framboids
, disseminated pyrites, rhizolithes, rhizocretions, calcimicrobes, and filamentous bodies argue for deposition in reducing environment and extensive anoxia lead to biodegradation of organic matter.
During the late stationary growth phase or death phase, the gold NPs which were initially precipitated inside the cells were released into the bulk solution and formed suboctahedral to octahedral, subspherical to spherical aggregates resembling framboids
, and ultimately millimeter-thick gold foil at longer experimental duration [148,149].
The SEM observation and microanalysis results indicated the presence of calcite, organic matter, and pyrite in the bulk lignite samples as framboids
and as isolated euhedral forms (Figure 4).