Tiger's eye in XPL - 2.5 billion year old banded-iron formation showing the birth of our oxygen-rich atmosphere #ThinSectionThursday

Nature's chocolate egg - a particulary brown agate nodule. Happy Easter from the Rock Library.

Ignimbrite with rheomorphic flow in rotated lithic clasts. Field petrology in Sardinia with Matthew Genge Peter Chlen Alessandro Chiarenza @peterophysics

Mantle xenoliths with pyroxenite veins and phlogopite megacrysts from Sardinia. Mantle fieldwork with Peter Chlen Matthew Genge Alessandro Chiarenza

Metagabbro...Silurian back-arc basin magma at greenschist facies. In Sardinia...with Matthew Genge Alessandro Chiarenza @peterophysics

Through cross beds in Triassic sandstones never fail to impress, particular in Sardinia. Alessandro Chiarenza Peter Chlen @peterophysics

Parallel agate-bearing vugs in a basaltic andesite sill injected into wet pyroclastics in Sardinia. Alessandro Chiarenza Peter Chlen @peterophysics

Rock library in the field. Spindle bombs and matle xenoliths from a leucite basanite scoria cone in Sardinia Peter Chlen Alessandro Chiarenza

The Rock Library's Matt Genge on the rocks of Australia House in London x.com/rockbloke/stat…

Lamproite from Oz with phlogopite phenocrysts in a groundmass with richterite and leucite. The world's deepest magma. #ThinSectionThursday

Like a knife through butter. Cutting a slice through a basalt with a mantle xenolith - using a rock saw to make a #ThinSectionThursday

F2 folds with crenulation cleavage in black phyllite and metasiltstone, Falmouth, Cornwall. #fieldworkfriday for the RSM's Paul Garrard

Every day the Rock Library is attacked by hackers. So sorry to all the students and staff who rely on us. We are repairing malicious damage.

Amphibolite with folded veins of quartz, feldspar and hornblende. St Paul's underground station, London. ImperialRSM

Normal faults in Triassic sediments on a wavecut platform east of Watchet, Somerset. Seeing geology by drone. ImperialRSM

Archean jasperite at Marble Bar, Pilbara, Australia. A 3.46 billion year old chert. ImperialRSM

Conical stromatolites in the 3.43 billion year old Strelley Pool Chert in Pilbara, Australia. Old critters! ImperialRSM

Ripple cross lamination with hematite in the 2.5 billion year banded iron formation at Paraburdoo, Pilbara, Australia. ImperialRSM

Pyrolucite (manganese oxide) in a synsedimentary breccia formed as an Archean palaeosol on dolomite. From Pilbara, Australia.

Gneissose banding and pegmatite in an Archean granite gneiss from the Pilbara craton, Australia. These diapirs squeeze the greenstone belts.