Microspherulites are microscopic spherical particles with diameter less than two mm, usually in the 100 micrometre range, mainly consisting of mineral material (the Greek litos means "stone"). Only bodies created by natural physico-chemical processes, with no contribution of either biological (in aqueous sedimentary environments this contribution is possible) or human activity, are considered to be microspherulites. Generally speaking, the common feature (sphericity) indicates that each sphere represents an internal equilibrium of forces within a fluid medium (water, air).

Several types of these forms are found in nature. Depending on the formational environment, microspherulites can be classed as oolites, micrometeorites, impact spherulites, iberulites, pisolites, aerolites, chondrules, biolites, pellets, bubbles, or carbonaceous microspherules.