“Your brother is good at producing slides for this, over in the rock cutting lab,” he said. “You take a thin section of rock — say, five millimetres. You polish it with carborundum, take some thin chips, stick them to glass with optical glue, and then polish them in a grinder until they’re no more than fifty microns thick. Thin enough to see through. The art is the finishing by hand that comes after that; you need better than five microns tolerance, and to get that you have to overcome faults in the jib you use, even in the glass slides themselves…”

She looked dubious. “I’m surprised they let you bring that thing in here.”

He looked at the microscope, through her eyes. It was kind of battered, he admitted. He’d picked it up for twenty bucks as an honours student when his department had a clear-out, and it had been old even then. But the mechanism still ran sweet as a nut, and the Swiss optics were as bright and clear as the day they were ground, and the “scope, worn smooth with use, had been all over the world with him.

Henry expected to be buried with his “scope.

Still, Mike had banned him from bringing its wooden box in here, which was even more disreputable.

He stepped forward to check the alignment. The view through the eyepiece was a disc of multicolored light, irregular shapes of bright colour. He twisted the analyser disc to show up the colours.

“Take a look,” he said. “Try to keep both your eyes open. After a while, you won’t see anything through your other eye.”

She bent, and turned the analyser as he showed her.

“What do you see?”

“It’s like a view down a kaleidoscope.” Jane straightened up. “Wow. I’m dizzy.”

“That’s your other eye cutting in. Forget it. The point of the “scope is that you can see what minerals are present there, just by letting the thin slice filter polarized light.”

“Just like that? At a glance?”

“At a glance. Neat, isn’t it?”

“What am I looking at? Your bedrock?”

“No That’s a reference sample. A lunar basalt from another suite, closer to the norm of the Apollo samples. Tell me what you see.”

She bent again. “Lots of small shapes, like a tiled floor. And, here and there, like pieces of stained glass window, rough discs and rectangles. Much larger shapes. Ships of glass, sailing among ice floes. As seen when on acid.”

He laughed. “What you’re looking at is a felted matrix of small elongate crystals of feldspar — that’s the grey stuff — pyroxene, yellow — and olivine, all the bright colours you can see, scarlet and yellow and pink and blue. And stuck in the matrix you have those bigger crystals, phenocrysts of pyroxene and olivine.

“Now.” He took out the slide, replaced it with another. “This is 86047. The bedrock. See if you can tell the difference.”