SpecialSetOfSieves

Thanks for posting this, Paul; I had meant to go through this year's abstracts more closely, so this saves me some time!

The image, aside from being spectacular and essential for visualizing this mission's progress, is one of those key diagrams that needs to be on a regularly-maintained "reference page" somewhere.

Personally, I'm fond of this recent shot of finely-banded material, or this interesting whitish-looking find, but... the wisdom of crowds, I guess.

There is just so much to see around here...

Question(s) for Paul Hammond:
Do you keep any rock specimens, personally? Would you find vesicular basalt to be charismatic enough to earn a place as one of your pet rocks? I see that you like these "shiny" or "polished" cobbles we've been seeing all mission long... I think... but we don't often analyze them in this much detail.

AHHH the suspense! Come on relay network, send us the next ones ASAP! I know those sats are busy too, but this wait is killing me.

I really wasn't sure we'd abrade here. I mean, we skip past funky-looking darker caprock all the time (for months at a time when Ken Farley is in a hurry)! Even when the rover can physically reach it. Just look at this stuff, it's craggy and lumpy as anything... but that flattish patch they're grinding: yes.

Even with all the evidence for volcanic deposits around here, I honestly wouldn't guess what this abrasion patch might show us. Volcaniclastic rocks like tuff aren't the hardest for sure, but this stuff forms the resistant layer here. We focus a lot on sampling with this mission, understandably, but I'd love to read more about the science team's deliberations over whether we do (or don't) stop and abrade stuff. We always abrade before we take a sample, so abrasions are just as important as samples in a lot of ways...

Apologies for the word salad. Paul Hammond knows my pain.

Judging by the rocks Percy has been viewing in the last few sols, this hillside has seen quite a bit of hot/volcanic material falling from the sky, and not just from a single asteroid impact either. The geology here is captivating.

In 2004, the Mars Exploration Rover Opportunity spotted so-called, “Martian Blueberries” at Meridiani Planum, and since then, the Curiosity rover has observed spherules in the rocks of Yellowknife Bay at Gale crater. Just a few months ago, Perseverance itself also spied popcorn-like textures in sedimentary rocks exposed in the Jezero crater inlet channel, Neretva Vallis. In each of these cases, the spherules were interpreted as concretions, features that formed by interaction with groundwater circulating through pore spaces in the rock. Not all spherules form this way, however. They also form on Earth by rapid cooling of molten rock droplets formed in a volcanic eruption, for instance, or by the condensation of rock vaporized by a meteorite impact.

See also this recent Mars Guy episode.

This is the second coring attempt at the very same target... with one sample already successfully extracted at this very spot.

They took only one sample at the leopard spots/Bright Angel/Neretva Vallis/potential biosignature site, but two here.

2025 is wild.

There has been a strong culinary theme on this instance lately.

I suppose that balances out with the fact that many conversations at LPSC this week have been about DOGE-induced famines.

My mama always said old crater rims was like a box of chocolates. You never know what you're gonna get.

Regular readers will remember the "white rocks" that Percy was spotting in little clusters a few months ago, which Mars Guy, among others, was speculating might be quartz. The paper confirms that the first rock examined in detail in the video does contain that mineral, and is not simply another whitish mineral you might expect to find in this environment, like gypsum.

Part of the significance of this mineral being identified is the fact that it seems to comprise most of the rock being analyzed. Quartz-like material ("silica") has been discovered by Spirit, Curiosity and even Zhurong, thousands of km away from Jezero Crater, and Percy itself has already identified some in Sample 24, which we grabbed down in Neretva Vallis. Finding this much silicon dioxide, in multiple forms, in a rock that appears silica-dominated, however, is something new. That's water activity on another level - this is basically very refined silica that nature has cooked up. As the paper mentions, it would be very, very sweet to find an exposure of the source bedrock for these loose pebbles and cobbles, because that stuff we could drill for return to Earth.

Shortest answer: quartz has to be separated from other rocks/minerals. Water action is one of the easiest ways to manage that. In addition, opal/chalcedony is actually quartz with water directly attached on a molecular level, so that's a direct discovery.

Medium answer: Igneous ("volcanic") rock already contains the silicon and oxygen that quartz is made of, but they're usually bonded with other elements, not just each other. In other words, they don't exist as "free quartz" - meaning independent grains that are made of pure SiO2. As @athairmor alluded to, free quartz can form directly from magma when it solidifies and forms igneous rock. However, that is what you would expect from particular kinds of volcanic rock, which are absent or rare on Mars (e.g. granite). The igneous rock around Jezero Crater is not the type to contain "free quartz". If the regional geology hasn't served up any free quartz grains directly, you can still separate out the silicon and oxygen by breaking down the larger, more complicated minerals they're attached to, but that would take a significant amount of chemical breakdown - i.e. significant amounts of water. This process is quite common on Earth, of course, where it yields up "white sand" on beaches - which is simply rounded grains of quartz.

Longest reply: I should probably just read the EPSL paper, and I'd be happy to summarize it here if people are interested.

So that means all four sampling attempts made here on Witch Hazel Hill have been difficult in some way. Two of the attempts were outright failures, the last successful one only filled half the tube, and this latest one, #27, "overflowing" to the point of rendering the seal difficult.

I count four "difficult" sampling operations from the entire mission prior to reaching the Hill (Sample 1 an outright failure, Sample 15 difficult to seal as Mars Guy refers to in the video, and two outright failures on the delta fan around sol 810-813), maybe five if you count that problem with the pebbles getting stuck in the bit carousel after successfully snagging Sample 6.

It may have taken 37 sols, but they finally did seal Sample 15, so I'm not overly worried about this problem with Sample 27. What I find striking about all of this is the intersection of the geology with the engineering. The problem we encountered with the very first sample (the stuff simply crumbling and escaping the tube before we could seal it) was a warning shot to the rover operations team, but a fascinating sign to the geologists: this stuff has seen some serious alteration since it was originally laid down! And that weak, friable Sample 1 material saw much less transformation by water, mineralogically speaking, than Sample 27...

We knew that we were going to find igneous ("volcanic") geology combined with sedimentary geology (old river mud and sandstone) on this mission, but the intersection of the two giving us these kinds of problems is going to become part of the legend of Mars exploration. It may not be as controversial or unexpected as the Disappearing Methane Hunt or the Viking-era "biosignature" tease, but this sampling difficulty shows us just how tricky Mars is going to be.