#dunite

Olivines from dunites from the Mid-Atlantic Ridge.

Olivine is a mineral group with the general formula (Mg,Fe)2SiO4 and usually found in igneous rocks like gabbro, peridotite, basalt, and dunite. It's abundant in the mantle.

okay, but hear me out. ultramafic rocks. 

The Xenolith Flow These barren rocks have sat on this site since 1802, when they arrived here after pouring out of Hualalai, one of the volcanoes that compose the main island of Hawaii.

The Kondyor Massif

While it appears to be a volcano or a meteorite impact crater, the 10km circle on the Siberian surface depicted in the photo is an intrusion of very low silica magma that rose up from the mantle over a billion years ago. It reached a buoyancy point in the Archaean meta-sedimentary rocks of the Siberian craton, stopped, and slowly crystallised (baking the rocks around it into a hard metamorphic rock known as hornfels). The surrounding ridge is 600 metres high, and the dome is gifted with an uncommon geochemistry that led to one of the world's major platinum placer (alluvial) deposits, located in the snowmelt fed river leading out of the feature. Located between Khabarovsk and Yakutsk in the endless expanse of Russia's far east, the dome was gradually exposed by the forces of erosion, though it took a billion years for the crust above it to be removed.

Those of you who have survived an igneous petrology class will probably have glanced at thin sections of places such as the Bushveld intrusion in South Africa. The complex is mostly made of dunite, a rock made of nearly pure crystalline olivine (aka the gem peridot, see http://tinyurl.com/pavuvbq), associated with clinopyroxenite. These intrusions often crystallise simultaneously from the outside inwards in layers, following a complex zoning dance ruled by the laws of physics and chemistry and the complex changing conditions within the magma chamber.

Last year it produced 4 tonnes of the metal, including unique specimens of a very rare alloy of platinum and iron, coated with gold that are found as nuggets in the river. Several rare platinum group (platinum, rhodium, iridium etc) minerals have been named from discoveries here, some unique to this site. Konderite is a mineralogical mishmash of copper, platinum, rhodium, lead, and sulphur, a testimony to its unique geochemistry and crystallisation conditions.

The image was combined from the ASTER instrument on NASA's TERRA Earth observation satellite, by draping a image date onto radar elevation data

Loz

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