She looked.

“No olivine.”

“To a first approximation, yes.”

She straightened up, frowning. “So what?”

He lifted his white hat and ran a hand through his hair. “So, that’s wrong. I can’t figure out what process has taken out the olivine here.

“Look — rock is made of silicon and oxygen, and other stuff. The basic structure formed by silicon and oxygen atoms is a tetrahedron. An olivine molecule is built around a single tetrahedron, with iron and magnesium atoms stuck on. So olivine is the most basic form, the mother of all silicates.

“Deep in the mantle, at high enough temperatures, olivine is all you find.

“But when a lump of mantle material rises and cools, more complex molecules can form. You put together the tetrahedra like building blocks. First you get pyroxene, which has single chains of tetrahedra, then amphibole, which has double chains, and then mica—”

“I’ve seen mica. Flaky stuff, thin, papery sheets that you can chip off with a fingernail.”

“Right. Mica is made up of sheets of the tetrahedra. But then, when the mica cools further, you have quartz. A three-dimensional lattice, a tough, hard crystal. So you are getting more and more complex silica structures, built of tetrahedra.”

“So what happened here?”

“I don’t know. It looks as if something has — accelerated the process, in this lump of Moon rock. Reworked the crystalline structure.”

“Reworked? How?”

“I’ve no idea. One tack we’re following is trying to replicate lunar mantle processes in the high-pressure labs.”

In these, he told her, you placed a small sample of your rock in a foot-high stainless-steel block called a bomb, and then pressurized it hydraulically, as far as twenty thousand atmospheres, which corresponded to pressures in the Earth’s mantle.

Sometimes the bombs failed, and lived up to their names. So the labs were run remotely, and had steel plates built into their walls, and blast chimneys.

But the high-pressure tests weren’t showing them anything they didn’t know already.

“In the meantime, we’re ordering up other studies. X-ray fluorescence work, and time on the ion microprobe they have here. That lets us study the composition of very small samples of the rock…” He scratched his head under his hat. “I’ll tell you something else odd. The samples I’ve been taking from the liquefaction patch, on Arthur’s Seat—”

“I’d like my bottle back sometime.”

“Yeah. I ran them through the “scope, and a couple of other tests. They are deficient in olivine as well…”

She frowned.

“I can’t see any connection either. Spooky coincidence, huh.”

But she was hesitating. As if there was something, some connection, she wasn’t telling him.

He said, “You know, if this — whatever — is consuming olivine—”

“What?”

“The Earth contains a lot of olivine, in the mantle. No wonder that patch is growing. And it isn’t going to stop eating either.”