| Igneous rock | |
 | |
| Composition | |
|---|---|
| Quartz; Alkali feldspar; Plagioclase; Hornblende; Biotite |
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.[1]
Almost one third of known orbicular rock occurrences are from Finland.[2] The occurrences are usually very small.[3]
- ^ Lindh, Anders; Näsström, Helena (September 2006). "Crystallization of orbicular rocks exemplified by the Slättemossa occurrence, southeastern Sweden". Geological Magazine. 143 (5): 713–722. Bibcode:2006GeoM..143..713L. doi:10.1017/S001675680600210X. S2CID 129709727.
- ^ Konopelko, D. (1 April 2006). "Lahti, S. (Editor) Orbicular Rocks in Finland 2005, with contributions by P. Raivio and I. Laitakari.: Espoo (Geological Survey of Finland) 2005. ISBN: 951-690-911-6. Price €30, 177 pp". Mineralogical Magazine. 70 (2): 238–239.
- ^ Kristallin.de: Orbicular rocks vs. Rapakivis