(An aureole is the zone surrounding an intrusion, which is a mass of igneous rock that solidified between other rocks located within the Earth).
Until the end of the 15th century, she is represented surrounded by a mandorla, or almond-shaped aureole; in the 16th century the mandorla was replaced by a cluster of clouds.
During formation of a contact metamorphic aureole around a granitic intrusion, hydrothermal fluids carrying elements such as iron, boron, and fluorine pass from the granite into the wall rocks.
Astronomers could then study the corona any day when the aureole, the bright ring around the Sun composed of light scattered by particles in the Earth's atmosphere, was not especially bright.
Dense atmospheric haze also produces an easily observable solar aureole, apparent as a very bright region immediately surrounding the Sun, with a gradual tapering off of brightness with an increasing angle from the Sun.
If the cloud is composed of a wide range of droplet sizes, then the aureole will be observed.
It is dominated by the monumental figures of the two saints and the bust of the Virgin in a mandorla, or almond-shaped aureole.
Under conditions of a very broad range of droplet sizes, the colours will completely overlap one another, giving rise to the aureole.
Because of the generally greater depth, this type of aureole is often superposed on a metamorphism at more normal pressure-temperature conditions, and the rocks may appear schistose and exhibit new thermally generated minerals on a preexisting assemblage.
The contact metamorphic rocks of the aureole zone often lack any obvious schistosity or foliation.
Rocks of the sanidinite facies are represented by small fragments of aureole materials that have often been totally immersed in silicate liquids or by the aureole rocks surrounding volcanic pipes.
