#geoscience

Parts of ancient Earth may have formed continents and recycled crust through subduction far earlier than previously thought. New research led by scientists at the University of Wisconsin–Madison has uncovered chemical signatures in zircons, the planet's oldest minerals, that are consistent with subduction and extensive continental crust during the Hadean Eon, more than 4 billion years ago. The findings challenge models that have long considered Earth's earliest times as dominated by a rigid, unmoving "stagnant lid" and no continental crust, with potential implications for the timing of the origin of life on the planet.

I designed and made button pins for my coworkers based on their program area as a parting gift...very fun to make I love buttons

Today's Specimen: Ametrine

Ametrine is a variety of quartz with areas of natural purple and yellow/orange colouration. It's name comes from the colours it produces, resembling both amethyst and citrine. Ametrine deposits can be found in Bolivia, Brazil, and India, with the majority coming from a single mine in Bolivia. It is ranked at about a 7.0 on the Mohs hardness scale. Alternate names for ametrine include: Bolivianite, Golden Amethyst, and Trystine.

it's a good thing I love walking. Otherwise I'd hate this more than anything.

36°C heat, with only the sun and ourselves to keep us company, we started walking up a slope toward the large marble quarry that Penteli is known for. Same marble that built the great monuments of ancient Athens, of course. On the way up we stop to look at a good outcrop of (ortho)gneiss from a metamorphosed granite, a sample of which is here on the left, rich in mica and thinly banded and sparklier than the night sky, metamorphic petrology has so cooked us that we all saw it's green and schistose and called it greenschist, lol.

Greenschist we did find further up the path, though it's mixed with marble, and we got told the (newfound) bit of geology wisdom that, actually, that term is pretty much useless due to the sheer amount of protoliths that can spawn it rendering the term kind of too vague. So this is actually a basaltic intrusion, metamorphosed to the greenschist phase (thus a "metabasalt"), turned schistose due to stresses, and bundled together with some nice white marbles, that metamorphosed alongside them.

The views in and from that quarry are beautiful, if only Mt. Penteli wasn't literally the most fertile ground for fires it'd be greener.

The metabasalt intrusions ultimately ruin the market value of the marble, so the quarry was abandoned. A student doing her dissertation, however, told us about its metamorphosis. The highest temperature reached was 350°C at 6-8 kbars, very close to the blueschist fascies and so in one sample they even found blueschist minerals like glaucophane. Greece is today where the ancient Tethys ocean once laid, and many terranes were subducted into forming the landmass of today.

We then went on a 5km hike up Mt. Penteli on a quest to see the general geology of the area. Essentially (and reductively,) the mountain is like a large anticline fold or an upside down U, with orthogneiss as the lowermost layer and strata of marbles and metapelite schist above. Of course, it's more complicated. Faults and folds have made the anticline nigh unrecognisable, the metapelites vary wildly in schistosity and they often mix with the marbles to form the sparkliest rock you'll ever see, a metamorphosed marl, and the basalt intrusions from earlier show up either schistose or massive or granular, along with dikes of quartz and calcite, and interspersed are pockets of more gneiss.

The climb to the (almost) top was beautiful, although doing it by foot at this weather sucked. The sun blazed unwaveringly and the view was stunning.