Nope, not a food thread.

Just wondering. What is the physical difference between frost and ice? Is it a matter of crystalline structure?

Frost is caused by water vapor condensing and freezing. Ice is liquid water freezing.

Thanks, wwh. That's a good beginning.

Now under the microscope--how are they different?

I learned something interesting the other night--I learned that all oxygens are not created equally. A geologist trying to determine whether the moon was ever part of the earth examined moon rocks and found that the oxygen contained in the rocks was the same as the oxygen in our own rocks. This realization upset a physicist who had hoped that the moon came to us from another source. I read that the oxygen on Mars rocks, for instance, is different in structure from our own oxygen.

Anyway, all of that has led me to wondering how frost and ice are different. And it is especially interesting to consider how water vapor and water are different, other than the obvious point about their being in different states, one gaseous and the other liquid.

I'm no chemist, so how can oxygen be different from oxygen?

the thought of the difference between liquid and gas makes me think of phase transitions, which are so cool.

Et:

Later today I'll go upstairs and get the book I read so I can summarize the oxygen information. I'd never realized that oxygen is a varied thing.

Here's a bit from the Britannica on frost:

"True crystalline hoarfrost is of two classes, one of which assumes columnar forms and the other of which assumes tabular, or platelike, forms. Generally the crystals of these two classes do not occur together on a single night; rather, one or the other will greatly predominate. Columnar or needlelike forms are found at the higher subfreezing temperatures, whereas plate crystals predominate under colder conditions. In their pristine state both forms are hexagonal crystals, the columns having a hexagonal cross section and the plates appearing as flat hexagons. Because they must grow outward from some supporting object, they rarely assume the perfect symmetry found in many snow crystals.... At very low temperatures, cubical crystals are sometimes found. "

Oxygen is one of the elements that always combines with itself. You can never have an O, only O2, et cetera, or a compound with oxygen and some other element(s).

All of the elements are mixtures of isotopes. For instance dating of ancient
objects is done by determining ratios of for instance carbon isotopes.
so conceivably the oxygen compounds on the moon might have a different
ratio of oxygen isotopes. I have forgotten too much chemistry to give more
detail.

The following quoted section is from Earth: Inside and Out, Edmond A. Mathez, Editor, 2001:

"Dr. Ranu's jaw dropped when he saw the data. Contrary to what he had expected, these new, high-precision numbers showed no difference between the composition of the Earth's oxygen and the Moon's oxygen....

The data compiled by Dr. Noom is called oxygen isotope data, and it is arrived at by studying the atomic composition of oxygen in rocks using a machine called a mass spectrometer. An element is defined by the number of protons it contains, and its atomic weight is determined by the sum of protons and neutrons in its nucleus. Isotopes are atoms with the same number of protons and different numbers of neutrons....

When rocks from the Moon were returned and analyzed, it was found that the isotopes of oxygen in lunar rocks were indistinguishable from the isotopes of oxygen found in rocks from Earth.

Why is this similarity between terrestrial and lunar oxygen important? Because evidence from meteorites shows that the oxygen composition of extraterrestrial materials depends upon where in the solar system they formed. This conclusion has recently been confirmed by analyzing Martian rocks hurled into space by asteroid impacts that eventually fell to Earth as meteorites. These Martian meteorites all have an oxygen isotopic composition distinct from that of the Earth--and the Moon."


This book, by the way, is terrific.