Majorite
Encyclopedia
Majorite is a type of mineral
found in the upper mantle
of the Earth. Its chemical formula is Mg3(Fe, Al,Si)2(SiO4)3. Majorite was first described from the Coorara Meteorite of Western Australia
and has been reported from various other meteorites. Mantle derived xenolith
s containing majorite have been reported from potassic ultramafic magma
s on Malaita
Island on the Ontong Java Plateau Southwest Pacific.
A significant property of majorite is that under conditions of high pressure and temperature as exist in the mantle the mineral tends to absorb and store oxygen
. However when the temperature and pressure decrease as would occur when the majorite is drawn up toward the surface of the Earth by convection currents the mineral breaks down and releases the oxygen. Recent research has suggested that the total amount of oxygen stored in majorite in the mantle is likely quite large and may in fact contribute to keeping the Earth's surface moist and habitable.
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
found in the upper mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
of the Earth. Its chemical formula is Mg3(Fe, Al,Si)2(SiO4)3. Majorite was first described from the Coorara Meteorite of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
and has been reported from various other meteorites. Mantle derived xenolith
Xenolith
A xenolith is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption...
s containing majorite have been reported from potassic ultramafic magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
s on Malaita
Malaita
Malaita is the largest island of the Malaita Province in the Solomon Islands. A tropical and mountainous island, Malaita's pristine river systems and tropical forests have not been exploited. Malaita is the most populous island of the Solomon Islands, with 140,000 people or more than a third of the...
Island on the Ontong Java Plateau Southwest Pacific.
A significant property of majorite is that under conditions of high pressure and temperature as exist in the mantle the mineral tends to absorb and store oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. However when the temperature and pressure decrease as would occur when the majorite is drawn up toward the surface of the Earth by convection currents the mineral breaks down and releases the oxygen. Recent research has suggested that the total amount of oxygen stored in majorite in the mantle is likely quite large and may in fact contribute to keeping the Earth's surface moist and habitable.