glomerulites

Glomerulites are spherical to sub-spherical aggregates of mineral grains that occur within sedimentary rocks. They commonly appear as rounded, clumped nodules in hand specimens or thin sections and can range from a few micrometers to a few millimeters in size. The term glomerulite is derived from glomerulus, meaning a small ball.

Composition and formation: Glomerulites are usually composed of microcrystalline carbonate minerals such as calcite or dolomite, although siliceous glomerulites are reported in some rocks. They are interpreted to form during diagenesis when mineral-saturated pore waters precipitate crystals around nucleation points, producing localized aggregates that later become cemented into the rock fabric. The texture is characterized by internal random packing of grains rather than the laminated concentric structure seen in ooids.

Occurrence and significance: Glomerulites are most often described in carbonate rocks (limestones and dolostones) but can occur in other sedimentary settings where diagenetic fluids are active. Their presence provides information about diagenetic conditions, fluid chemistry, and pore-water evolution, and they can influence rock porosity and permeability. Distinguishing glomerulites from similar globular textures such as peloids or ooids relies on the lack of concentric laminations and the more clumped interior.

See also: glomerulitic texture; peloids; ooids; diagenesis; carbonate rocks.