Other snow
December 11, 2015 9:45 AM Subscribe
The kids and I were making paper snowflakes. We watched some snowflake videos. I showed them folding steps to make classic six-pointed or twelve-pointed paper snowflakes. They in turn rediscovered four and eight-pointed paper snowflakes. They asked, "Are there any real snowflakes that don't have six points?"
I thought of pyrite cubes and lead compounds, and recalled bits of how molecular bonds influence crystallization. Searching turned up pretty bismuth lattices and talk of hydrocarbon snow on Titan and lead sulfide snow on Venus. Ash and particulate pollution are so much in the news. But I couldn't find anything closely resembling H2snow with its planar tendency and consequent tumbling flakes that bring us such delight and dread. Can anyone find examples of snow-like phenomena that are not regular water snow?
I thought of pyrite cubes and lead compounds, and recalled bits of how molecular bonds influence crystallization. Searching turned up pretty bismuth lattices and talk of hydrocarbon snow on Titan and lead sulfide snow on Venus. Ash and particulate pollution are so much in the news. But I couldn't find anything closely resembling H2snow with its planar tendency and consequent tumbling flakes that bring us such delight and dread. Can anyone find examples of snow-like phenomena that are not regular water snow?
Best answer: Skimming the list of ice phases, Ic (diamond lattice) catches my eye: at 1 atm and lowish temperature, the equilibrium arrangement has four-fold symmetry, as against the six-fold symmetry of ordinary ice (Ih). Perhaps (contra Rob Rockets) this could lead to four-fold snowflakes? It would seem that Ic can form in the conditions of the upper atmosphere.
This isn't quite your question, though, as I understand it: you're looking for other compounds that are known to form interesting snow-like structures. That's a very, very interesting question, but not one I know an answer to. Graphene comes to mind (as it will), but
posted by golwengaud at 10:13 AM on December 11, 2015
This isn't quite your question, though, as I understand it: you're looking for other compounds that are known to form interesting snow-like structures. That's a very, very interesting question, but not one I know an answer to. Graphene comes to mind (as it will), but
posted by golwengaud at 10:13 AM on December 11, 2015
Best answer: Clay minerals like kaolinite and chlorite have a planar, hexagonal structure and in the right circumstances will "fall" like snow, particularly in water, leading to silt deposition. One particular kind of clay called bentonite frequently forms when volcanic ash falls into water - typically marine but often lacustrine - and falls to the sea floor.
The carbon composition depth line is the depth in the ocean when carbonate minerals go into dissolution. In oceanic areas with topography we find what's called the "snow line" where the deposition of carbonate occurs above the line; although technically the minerals involved are not planar, if there is significant clay involved you do see carbonate-clay deposition like chalk, which can be quite planar or chaotic.
Technically, I would consider sand dunes the result of a tumbling action - called saltating - and a sand dune composed mostly of weathered minerals from granitics can have some planar minerals, even layers of them.
Also, while technically not planar or of a singular composition, marine snow is the steady fall to the seafloor of biogenic material like fecal pellets and dead plankton, as well as minerals (and in composition involves the CCD but in definition is a different thing).
As for straight up mineral structures like snowflakes, certain kinds of plankton form very snow-looking structures from calcite.
posted by barchan at 10:26 AM on December 11, 2015 [3 favorites]
The carbon composition depth line is the depth in the ocean when carbonate minerals go into dissolution. In oceanic areas with topography we find what's called the "snow line" where the deposition of carbonate occurs above the line; although technically the minerals involved are not planar, if there is significant clay involved you do see carbonate-clay deposition like chalk, which can be quite planar or chaotic.
Technically, I would consider sand dunes the result of a tumbling action - called saltating - and a sand dune composed mostly of weathered minerals from granitics can have some planar minerals, even layers of them.
Also, while technically not planar or of a singular composition, marine snow is the steady fall to the seafloor of biogenic material like fecal pellets and dead plankton, as well as minerals (and in composition involves the CCD but in definition is a different thing).
As for straight up mineral structures like snowflakes, certain kinds of plankton form very snow-looking structures from calcite.
posted by barchan at 10:26 AM on December 11, 2015 [3 favorites]
Very different shape, and frankly best kept in a sealed bottle: menthol crystals. They sublime really easily, so you'll end up with a bunch of crystals growing inside the top of the bottle, with no obvious link to the other crystals. They're pretty needle-like crystals, but not things you want near skin, eyes, or pets.
posted by scruss at 10:28 AM on December 11, 2015
posted by scruss at 10:28 AM on December 11, 2015
And I just realized I answered your kids' question above the fold and didn't even address your question below the fold. My bad. The closest similar phenomenon I can think of is volanic ash falling back to earth, like when Mt St Helens erupted
posted by mattamatic at 10:32 AM on December 11, 2015
posted by mattamatic at 10:32 AM on December 11, 2015
Response by poster: Thanks, all, for identifying limits for water snow and leads to non-water snowlike phenomena.
posted by gregoreo at 6:25 PM on December 12, 2015
posted by gregoreo at 6:25 PM on December 12, 2015
Response by poster: As for water snow, this December 2014 Smithsonian article links to some more nearly thorough recent analyses.
posted by gregoreo at 4:15 PM on December 23, 2015
posted by gregoreo at 4:15 PM on December 23, 2015
This thread is closed to new comments.
posted by mattamatic at 10:04 AM on December 11, 2015