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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.
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References in periodicals archive ?
For the oncolitic deposits of the Higueruelas Fm, the description of the microfabrics observed in the oncolitic laminae is based on the terminology used by Dahanayake (1977) for the Kimmeridgian oncoids of the French Jura Mountains.
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.
Microherms in the Smackover consist of concentrically laminated (stromatolitic), clotted (thrombolitic), calcimicrobial, or structureless (leiolitic) carbonate, and texturally resemble associated oncoids (algal balls).
The oncolitic limestones are characterised by grainstones of oncoids (19 mm in diameter) with small colonies of corals.
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.
Locally, this microfacies includes foraminifera (Andersenolina and Nautiloculina) and some oncoids. Small quartz grains constitute a minor component.
These carbonate rocks formed during the maximum transgression of sea in Early Frasnian time and are rich in fauna (brachiopods, pelecypods, gastropods, cephalaspods, corals, stromatoporoids, stromatolites, oncoids and fishes; Sorokin 1978; Stinkulis 1998).