So now that we’ve been here for two solid years - that’s four whole years back on Earth! - after we’ve driven across the floor and over the delta and into the valley and all the way up the rim - NOW you decide you want a pet rock? After His Lordship has decided that he’s going to tariff anything Martian?

sighs He’s always like this with the shiny ones. He thinks it might be desert varnish. You think it’s desert varnish, don’t you? Do you know what’ll happen if we actually do find any of that stuff? The handling procedures. The import licenses. The biohazard protocols! Endless arguments over G-band spectroscopy from the damn scientists, they’ll be at it for years. How are you going to feel if your small rock happens to be the first with active biological entities? Come on, that’s the last thing we want.

I can’t take you anywhere, Paul.

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.