It’s also known as Orbicular Granite or Orbiculite. It’s a name received by all the plutonic igneous rocks that have a special radial texture. These rocks originate in deep magmatic processes with gradual cooling and gradual formation of crystals. They occur in all types of composition from granitic to mafic, ultramafic and carbonatic rocks.
All of these rocks contain a core in the middle surrounded by radially grown crystals that transition to outer concentric lines called shells. These shells are composed of different layers of crystals. Some layers are of radially grown crystals (often plagioclase), some are tangential and others are composed just of small grains without any orientation.
The most famous places with orbicular granites
- Caldera, Chile
- Kuru, Finlandia
- Mount Magnet, Australia Occidental
- Savitaipale, Finlandia
- Slättemossa, Hultsfred, Suecia
- Karamea (Nueva Zealanda)5
- Cape Geology en Granite Harbour, Estrecho de McMurdo, Antártida
- Taylor Valley en la Antártida
- Sierras de Córdoba en República Argentina
- Santuario de la Naturaleza Granito Orbicular
6 en Chile
- San Juan La Laguna en Guatemala
The Drawing above shows the typical texture of an orbicule from Pengonpohja/Kuru- Finland. The Orbicul is dominated by shells that show different ways of texture.