Spherulitic

Spherulitic refers to a texture characterized by roughly spherical aggregates of radiating crystals, typically crystals growing from a common center and extending outward in a sunburst pattern. The term is used in geology and materials science, with emphasis on radiating crystals rather than composition.

In geology, spherulites are sub-spherical to spherical masses composed of radiating crystals embedded in a glassy or microcrystalline matrix. They are common in volcanic rocks such as obsidian, rhyolite, and andesite, and form during devitrification of rapidly cooled melts or crystallization within glass. Quartz and feldspar are common constituents; sizes range from micrometers to millimeters. Spherulitic textures can resemble vesicles or phenocrysts but are solid, radiating crystal aggregates rather than hollow voids.

In polymer science, spherulites are spherical, radially symmetric crystalline bodies that grow from a central nucleus as semi-crystalline polymers crystallize from melt or solution. They exhibit birefringence under polarized light and can produce characteristic interference patterns, such as the Maltese cross in many polymers. Their size and lamellar arrangement influence optical appearance and mechanical properties, including toughness and clarity.

Formation and controls: spherulites form during cooling or solvent evaporation when undisturbed crystallization proceeds from a nucleation center. Factors influencing size include cooling rate, degree of undercooling, presence of nucleating agents, and impurities. In rocks, spherulites can be mistaken for vesicles or phenocrysts.

Etymology: derived from Greek sphaira meaning ball and lithos meaning stone. See also devitrification, radiating texture, porphyritic textures, glassy textures, polymer crystallization.