Description

Orbicular granite (also known as orbicular rock or orbiculite) is an uncommon plutonic rock type which is usually granitic in composition. These rocks have a unique appearance due to orbicules – concentrically layered, spheroidal structures, probably formed through nucleation around a grain in a cooling magma chamber due to rapid physical changes. Almost one third of known orbicular rock occurrences are from Finland. The occurrences are usually very small. Orbicular granite is a unique and visually distinctive type of granite characterized by the presence of orbicular (rounded) structures or concretions within the rock matrix. These orbicular structures are composed of concentric layers of minerals, creating spherical or ellipsoidal patterns that stand out against the background of the granite. Orbicules can range in size from a few centimeters to several meters in diameter.

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