#phdee

All in a night's work – 1 am in the lab sieving and olivine crystal picking. Started with the easiest of my samples, as there there was only one major phenocryst phase to look out for (olivine; see thin section below) and I didn't need to discriminate between ol, px and plag under the binocular microscope (yet). I will be studying olivine hosted melt inclusions down the line – these olivines are chock full of spinel inclusions (black dots in the olivines) though I'll have to see if I can find any glassy MIs. Reddish colouration of olivine is oxidation to iddingsite (usually) at the rims.

That said I am not made for such careful work! Basically sorting sand and silt grains! Accidentally flung a full dish into my lap one time, and have lost several soldiers from tweezer flinging throughout the night! My hands are not steady enough for this!

6 hours of olivine picking today (and I managed to catch quite the sunset on my way out of the department). Having exhausted my olivine-only phyric samples, and having gained what I believe is a sufficient understanding of what olivine looks like under the binocular microscope and how to distinguish it from other phases, I have now moved on to some of the cooler samples. This is from a plagioclase megacrystic flood basalt unit in Ethiopia, which I thought was going to cause me some trouble but instead proved to be chock full of (hopefully usable) olivines. The pale crystals are plagioclase, and under the light their cleavage planes are often visible. The greener ones (collected) are olivine, though some of the plagioclases have a greenish tinge (likely parts of plag-ol crystal clots). I believe the pyroxenes are restricted to the groundmass, but we'll see when I have a look under the SEM-EDS after I've mounted my crystals. The grey bits are groundmass - very finely crystallised material with the residual mineral phases that crystallised on eruption/rapid cooling (vs the larger phenocrysts, which crystallised at depth).

Highlights include a museum collections visit, where I had a look at a bunch of samples collected in the 1930s (will hopefully be analysing said samples down the line, after I get the necessary permissions). Balking at how I spent a full year in futility searching for teeny tiny ridiculously rare melt inclusions in my flood basalt samples, only to pop one of these sections under the microscope and literally land on a massive MI. Which set the tone for the rest of the day; some 25 samples chock full of ol and px hosted MIs.

Bought a kids binocular microscope for about £40 so I can do some sample prep at home. Verdict: it's not bad! This is entirely sufficient for crystal picking (the most mind numbing of tasks which is generally best done in front of a TV). I may also see if I can buy an ultrasonic jewellery cleaner as I'll be able to do some sequential polishing that way. I'm hand polishing to 1um and use lapping film which is easily done at home. The only things I need and can't do are hot plate work and checking crystals under reflrcted light. But if I can do most things then I can cut my time in the lab by a LOT and I need that right now. Also since I'm prepping them for rehomogenisation I do not need to actually polish through to the MI (for which reflected light is necessary) - I just need a sufficiently clear window to work with.

Hello, EDS maps.

A bunch of thin sections imaged using under the SEM (scanning electron microscope) and then overlain with elemental EDS data in false color composites.

The dark blues are olivines, being FeO (red) /MgO (blue) rich; cyan crystals are diopside pyroxenes, being CaO (green) and MgO (blue) rich, and the pink crystals are Fe-Ti oxides, being FeO (red) and TiO2 (pink) rich. The very green groundmass in some samples is probably plagioclase, which is compositionally quite different from the cyan groundmass of other presumably more pyroxene rich samples. (These are foidites)