Geograph - photograph every grid square

Unit 7/8 - Eastern Layered Intrusion

Included fragment/xenolith?
None of the above, in fact this is a really interesting bit of geochemistry. The 'white' rock is troctolite, a plagioclase (feldspar, calcic) rich gabbrotic rock. The orange blobs are peridotite, a rock with a high olivine content. A thin black layer surrounds the peridotite, this is chromite. This feature is a plan view of unit 7 troctolite with the base of 8 being the chromite/peridotite.
In the magma chamber the crystals being formed were mostly plagioclase with pyroxene (clino) along with minor olivine. A new injection of pictite basalt from below meant a layer of picrite at the bottom on the chamber, this didn't mix due to a higher density. So it cooled, crystallising firstly chromite before olivine. These rained down and settled (cumulus texture) this lowered the density of the pictite basalt resulting in mixing, the crystallisation continued. Iron, magnesium and other elements are locked up in the olivines so the chemistry of the liquid changes to a more silica rich, potassium rich calcic melt. Plagioclase and pyroxenes form more easily and more often resulting in the change from peridotite to pyroxene gabbros then troctolites and anorthosites. This has created the layered effect.
The chromite was so hot when it rained down (around 1125 degrees Celsius I think) that it burnt out the floor (troctolite crystal mush) causing sag deposits.