Microscopes and minerals in Aberystwyth

Looking forward to the weekend...

Short days, dark mornings, it's the time of year for our annual 'lab weekend' in Aber. We used to use the university labs in Llandinam Builhasn't abut they got greedy, so last year we tried out a room in the hotel. It workin geard well for the mapwork in 2014, so this year Charlie and Bill are bringing down the microscopes and thin sections for us.

Wednesday evening... 

just heard that there's been a bit of a muddle over the room booking at the hotel, they thought we only needed the room Sunday. Fortunately Jan has got it all sorted though it means Saturday morning is in a different room.

2014 Mapwork weekend at Park Lodge, Aberystwyth

Thursday...

Keeping an eye on the weather, OK here in the SW Midlands. But hope people aren't coming from Manchester way and points north as I hear it is snowing there.

One more day to go

Friday - heading for the snowfields!

 Luckily the snow was the right kind - the kind that stays on the hills, not on the road (though some edges were a bit white)

 Lovely views though, this lone tree on a hillside (yes, it was at that angle)


And lovely contrasts between dark clouds and sunlit hillsides

 Stopped for a breather at Gilfach where there's a pleasant pull in off the road and found this new sculpture of a salmon

Finally ended up at Ynyslas for out picnic and a brisk walk on the sands - blowing hard!

Jan is well ahead, looking for the sea!

Saturday...

Lovely fish pie for dinner last night, and almost everyone has turned up now: met the stragglers at breakfast time, all apart from one lady. We are rather concerned that she hasn't arrived yet. Usual lovely breakfast... starting at 9am.... time to get head in gear! Though Jim asking me what orthorhombic, triclinic etc meant, over my bacon and tomatoes, did help...

Crystallography from basics this morning, looking at crystal structure, unit cells etc and then onto symmetry,

Coffee at 11 was a very welcome caffeine boost before an "aside" when Charlie proved geometrically that only a limited number of symmetry axes can exist! Might read that bit again later.....

Charlie and Bill conferring

In the afternoon we explored crystal shapes and symmetry, and were introduced to concepts of "form", "zones", and crystallographic axes before moving on to Miller indices.

Kath explaining things to Becka

By the end of the afternoon we were ready for an hour out before the evening lecture from Nick Pearce who uses lasar ablation techniques on tephra to help date archaeology in a talk entitled "Finding the sources of far travelled geological and archaeological materials".

He discussed graphical techniques used to differentiate between different eruptions of the super volcano of Toba in Sumatra, and then moved nearer home to look at sources of some of the foliated rhyolites in amongst the Prescelli bluestones at Stonehenge.

Linda puzzling out symmetry 

Lots of questions, and the discussion continued over dinner afterwards.

I asked Nick about the rhyolite quarry in the Prescellis as it would have been interesting to look at it when we are in Pembrokeshire with John Downes in May but unfortunately it has been covered up until they dig again in September, and all that can be seen is the crag at the back that the stones may have been levered off.

Tomorrow the microscopes come out!

Sunday

Renewed enthusiasm with the sight of the microscopes! 

And, just in case you don't know what geologists use microscopes for, it is to look at rock thin sections like this one: 30 micron slices of rock (this is a garnet gneiss a bit like the one on the hotel bar - below).

Rock this thin is translucent and, because all the different minerals that go to make it up have different atomic structures, they refract (bend) light in different ways. Add polaroid sheets and you can get some interesting colours which help to diagnose the minerals.

My pet Rock Dragon, Craig, had a go: I told him he didn't need his hard hat and hammer indoors but like so many geologists he can't bear to be separated from them ;)

After he had had a go, he let organiser Jan A-J have a go too.

Jan A-J

We had a number of "tasks" to do, interspersed with explanations and mini-talks from Charlie. 

Some of us experimented with taking photos "down the spout" of the microscopes, and one, Lyn, had borrowed an eyepiece attachment that would link to her laptop.

Lyn and her USB laptop attachment

We spent all day looking at various thin sections and learning about what we were seeing and I took quite a number of photos, just a few shared here:

This is quartz, viewed through the polariser, and showing what's known as wavy, or undulose extinction. Normally, as you turn the microscope stage, a mineral grain goes completely black four times in 360 degrees. However, if a grain has been strained, like this one, it doesn't all go black at ones, but in patches.

This is just seen with normal light: you can make out the
outline of the crystal grain

This was my favourite though: an "hour glass twin" of the mineral clinopyroxene.

When crystals grow, sometimes grains of the same mineral grow together but with their atomic structure in different orientations. Here the blue "hourglass" is at a different orientation, and shows different colours in polarised light from the rest of the crystal grain.

This is in polarised light with the "twinned" part of the crystal
showing bright blue

Some people had long drives home, and the group began to thin out mid afternoon, finally winding up at about 4pm when Bill and Charlie, Jan and I, joined by Charlie's partner Angie, went off to the bar for a well earned beer before taking the microscopes etc down to their cars to go back to the university.

We talked over some plans for 2016: the exact weekend depends on the dates of Six Nations Rugby fixtures (geologists seem keen on rugby), but we've already got a tentative programme sorted out incuding microscope work on Saturday, and then stereographic crystalography on Sunday. Stereonets are a way of projecting a sphere onto a flat surface. I've only ever seen how to use them for analysing fault movement.... 

Monday morning, cold and rather dull, Jan and I headed home to Hereford, With a coffee stop at Rhyader where they don't seem to realise Christmas is over!