MORPHOLOGY, INTERNAL STRUCTURE, AND ORIGIN OF GLAUCONITE PELLETS

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SUMMARY

Glauconite pellets exhibit considerable variety in morphology and internal structure. Recognized morphological types are: (1) ovoidal or spheroidal; (2) tabular or discoidal; (3) mammillated; (4) ellipsoidal; (5) vermicular; (6) composite; and (7) fossil casts, internal molds, or replacements. Types of internal structures include: (1) random microcrystalline, (2) oriented microcrystalline, (3) micaceous, (4) organic (?) replacements, (5) coatings on detrital grains, and (6) fibroradiated rims.

These characteristics can be used to interpret the origin and/or subsequent history of pellet types. Suggested origins include: (1) chemical precipitation, (2) expansion and alteration of detrital mica, (3) alteration of fecal pellets, (4) alteration of clay fillings of fossil tests, (5) mechanical aggregation, and (6) chemical replacement.

Not all glauconite pellets exhibit diagnostic characteristics with regard to their genesis. Original morphologies may be obscured by abrasion (reworking) prior to final burial. Internal structures may be changed by recrystallization or other diagenetic processes.

It is concluded that glauconite pellets have multiple origins. They can form from several different parent materials and by several different processes. Frequently, however, characteristics which might reveal the original nature of the pellets have been lost during reworking and diagenesis.

Inasmuch as glauconite occurrences differ in kind and variety of pellets, recognition of pellet types and their distribution is potentially useful for stratigraphic correlation or environmental determinations.

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