The upper Maastrichtian organic-rich sediments studied at Gabal Oweina, Egypt, are moderately enriched in syngenetic
and diagenetic pyrite. Pyrite occurs mostly as layers or bands, group of lamina, lenses, diagenetic intercalated pockets, burrow
fills and disseminated individual pyrite framboids and crystals within the host sediments. The pyritic thin bands and lamina
consist mostly of unconsolidated to compact-oriented pyrite (oriented along the bedding planes) in gypsiferous–clayey matrix
and less common as poorly oriented pyrite crystallites. In several cases, pyrite crystals of the latter type depict zoning, fracturing
and micro-concretions. Pyritic burrow fills are composed mainly of pyrite, phosphatic ooids, microfossils, glauconitic
grains, poorly graphitized carbon and native sulfur. Pyrite replaces minerals other than gypsum, sulfur or carbon. It also
replaces microfossils thus turning some of the phosphatic ooids and microfossils to pyritized pseudomorphs. None of the
studied phosphate ooids or framboids contains any mackinawite, pyrrhotite or greigite. Based on the microscopic and
SEM observations of the micro-textures of disseminated pyrite found at Gabal Oweina section, four morphological forms
of primary pyrite could be identified: (1) Grouped multiple-framboids; (2) Individual framboids; (3) Pyrite idiomorphic crystal
overgrowths on framboids and (4) Single and aggregates of euhedral pyrite crystals. The multiple-framboid formation may
have emerged from three successive processes: nucleation and growth of individual aggregates of the microcrystals to form
combined micro-framboids (the growth of framboids); and followed by grouping of the several pyrite framboids. Direct pyrite
nucleation (shell formation), crystallization, and aggregation processes might complete a single framboid. The disseminated
single and aggregated euhedral pyrite crystals bear evidence indicating that their formation was via nucleation and growth of
pyrite crystallites and their aggregation (to individual framboids), infilling (in the interstices by additional pyritic material),
compaction and homogenization (of all these materials). Furthermore, we encounter for the first time in nature idiomorphic
pyrite crystals that integrated numerous framboids, using them as their nucleation and growth sites without erasing or modifying
their pristine morphology. Elemental sulfur contains minor concentration of Sb, Ni, Cd and Cu strongly suggesting
their presence as submicron sulfide crystallite inclusions. SEM and microprobe investigations revealed that goethite is present
as a weathering product in all morphological types of pyrite however; only an iron-sulfate (presumably melanterite) was
encountered as oxidation product of the multi-framboids and the euhedral aggregate crystals. The upper Maastrichtian sediments
not only contain a menagerie of pyrite morphologies but probably a complete record of the formation process and the
geochemical conditions of the growth of framboids, single pyrite crystals, pyrite burrows, pyritized Mn–Fe-oxide framboids
and finally their weathered products. The various pyrite forms strongly suggest a multistage process that led to their formation
without any evidence for mackinawite, pyrrhotite or greigite, precursors. There is also no evidence in the Oweina sediments
for post pyrite formation of mackinawite, pyrrhotite or greigite. The presence of elemental sulfur containing minor