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A spherical stromatolite that usually forms around a fragment of detritus such as a piece of shell or a grain of sand.

[Greek onkos, mass; see oncology + -lite.]

on′co·lit′ic (-lĭt′ĭk) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
References in periodicals archive ?
Oncolitic deposits (F1) of the facies subassociation A1 are interpreted as deposited in subtidal oncoid shoals which migrated in a carbonate platform and under normal marine salinity waters, due to their fossil
In the transition zone, 1 to 3 cm of oncoid packstone grade up into coarser microhermal packstone.
At the lamproite-oncolitic limestone contact, all the sparitic cement and the oncoid edges were re-emplaced by a new generation of carbonate crystals (Fig.
They exhibit stromatolitic, microphytic thrombolytic facies with sedimentary fills, oncoids, oncolites, pesoids, lithoclasts and intraclasts.
The one-meter tall stromatolites are marine in form, occur immediately adjacent to shore rather than in deeper water, are covered by a peat and soil with inter-head areas filled with a complex stratigraphy, are colonized by living freshwater mussels on their sides, appear to rim cenotes, and have oncoids in the sand flats surrounding the field.
The oncoids, as large as 2 cm, typically have a bryozoan, stromatoporoid or brachiopod shell fragment as nucleus, encrusted with Girvanella and Rothpletzella.
Also oncoids with tubular structure as fine micrite precipitated on filaments (calcified filaments) are seen (Fig.
Towards the eastern part of the section, it grades into 10 to 20 cm thick beds characterized by better sorting and a decreasing proportion of oncoids and micritic matrix (Fig.