I’ve been on a little internet ramble. The topic is aragonite, a form of calcium carbonate. Here are some pictures of inorganic crystaline aragonite, though mostly this post is about biogenic aragonite in sea shells.
I began with the following bits of knowledge:
Aragonite is one of two*/** polymorphs. In terms of minerals, calcium carbonate has two polymorphs: calcite and aragonite. That is, both are calcium carbonate, but they have different crystal structures, and are thus considered different minerals.
It is metastable. I also knew that aragonite is metastable (that is, stable under very limited conditions, and easily nudged into instability).
It occurs in sea shells. I recently learned that aragonite occurs in sea shells and corals, and was curious why an ‘unstable’ mineral would be useful in a biological setting. Is it common in shells, or is it rare? Does it have advantages over calcite? Or is it just easier to synthesize?
Our not-much-of-a-winter has passed, notwithstanding a few flakes eddying about in the gusty air today.
I went for a run along Minihaha Creek yesterday. The ice is entirely gone, and the muddy spots from the last snowmelt are dry. We’ve not had much in the way of moisture, either snow or rain, and I’m told 80% of the state is in drought conditions. We shall hope for a moist spring, though not so moist as to bring disaster upon the farmers.
It is interesting to look through the columns of the forest, and see, here and there, a tree hanging onto last year’s leaves.
After a long unusually warm period, we’ve had a brief period of cold and snow. The creek is still flowing free in most parts, and ice is mostly opaque white granular frozen shelves that protrude from either bank. However, there are areas where recrystallization has occurred, often, though not exclusively, under bridges, and often, though not always, showing signs of melting/refreezing.
Here we can see melting refreezing, with the fine-structure of the crystals erased, and only the large acicular macro-crystals visible.
refrozen acicular crystalsrefrozen crystals
Something else that interests me is that many of the masses of crystal, both refrozen and ‘fresh,’ have lots of empty space in them. You can see that a little in the image on the upper left; it is more visible in the photo just below. In a book I’m reading, Above the Trees, about the alpine tundra environment, it describes how sheets of ice form across the tops of small depressions, which then act as miniature greenhouses, warming the air below them. I wonder if heat rising from the flowing water is likewise trapped by the panes of ice above them, forming these honeycomb patterns of ice and air.
Sheets of ice, and the acicular crystals, often seem to me at an angle to the surface of the water of about 10-15°. On possibility is that the water in the deeper part of the creek is warmer, and so that there is a temperature gradient that affects the level at which ice crystals grow over the water. I think, but am not certain, the the ice crystals on either bank of the creek angle away from the water as they project out over the stream.
‘honeycomb’ of acicular crystals and plates
Finally, although much of the ice is refrozen, there appear to be areas of fresh crystals, or at least crystals that still show fine structure on the surface. One of the images below (right) is from under a bridge, where I would expect it to be cooler and sheltered from the sun, but the other (left) is from a more normally exposed area of the creek.
mat of acicular crystals with fine structureacicular crystals and plates
The image shown on the left is particularly interesting because it retains a lot of fine structure — etchings and dendrites — on the crystals. More detail below.
We continue to have above freezing weather during the day, dipping below the freezing point at night. The leads to a lot of melting and re-freezing on the creek. There are areas where the creek is entirely frozen over, and others where it runs free, except for a fringe along its edges. The ice itself is quite varied. Some is clear, some an opaque white; some has a dull granular texture, some is a palimpsest of crystals upon cyrstals
We are in the midst of an unusual warm spell. It is not unusual to have a few days of above-freezing weather in January – enough to melt the top layer of snow and ensure that in a few days everything will be a sheet of ice through Februrary – but this is different. It reached the fifties yesterday, and came close to that today. Almost all the little snow that we’ve gotten is gone. The brown grass is showing hints of green, and the bare trees have visible buds visible. Any more of this warmth and bulbs will sprout and buds will burst, and then cold will return and kill them.
I returned to Minihaha Creek five days after my previous visit for a run, and a look at the ice. The snow, not very deep before, has receded, and the fallen leaves arch above its surface, leaving a myriad of little cave-lets speckling the surface. I wonder if there are any organisms — macro or micro — that are adapted to take advantage of these niches.
We had a nice outing today. The main event was the play ‘Art’ at the Guthrie.
‘Arts,’ a play by Yasmina Reza, is not about art per se, but rather a satire on friendship, and the dynamics of the power structures that underlie, or perhaps constitute, friendships. The play begins with a purchase of a modern painting – all white – by one of the trio of friends, and the ensuing reactions of the other friends. While the art purchase is that catalyst, it quickly becomes clear that what is at stake is really the changing relations between the friends. Although there are a lot of funny moments, the deepening disagreements and the vehemence with which they were conducted brought ‘Who’s Afraid of Virginia Wolfe’ to mind. The acting was excellent, particularly that of Max Max Wojtanowicz who played Yvonne, the ‘buffoon’ of the group. The lighting and sound design was also excellent, in particular in signaling moments of solliquoy by the various characters.
We’ve had a remarkably long fall. Although we’ve had some chilly periods, the temperatures are still tending to edge above freezing during the day, and in the last month we’ve had days that make it into the forties, and even the fifties. We’ve had two light snows: one but a dusting, and the second perhaps an inch, enough to almost bury the downed leaves. So the world is mostly gray and brown: the dully gray winter sky arches overhead, and the grass, trees, and carpet of leaves is brown brown brown. Very dull.
I have been waiting, with anticipation, for the first ice crystals to form on Minihaha creek, where I do most of my runs. I enjoy looking at ice on the creek as the winter progresses. First, most of the water is open, and a crystalline fringe forms along the edges of still portions of the creek. Next, the fringes grow, meeting in a delicate and parlous surface in the middle. As the cold deepens, the ice thickens. In the early part of the winter the ice tends to be crystal clear — although depending on the way in which the crystals form the may make portions of the surface matte white.
Happy March 1st! There are now some cracks in the shroud of winter. Oftentimes, it seems to me, there is a period of a few days, usually in February, where the birds suddenly become more active. It is perhaps the first real hint of spring — real, in contrast to the phantom spring thaw that often happens in late January.
The winter here has been weird – a couple of sub-zero weeks, a couple of warmish (32ish) weeks, repeat. I run several days a week, mostly along Minihaha Creek, which winds through south Minneapolis. With the variations in temperature there is a lot of thawing and refreezing, and that, combined with changing water levels in the creek, results in marvelous ice crystals. Mostly they are two dimension intergrowths of needle-like crystals, almost fabric-like in their structure.
Yesterday morning I went down to the kitchen, and in the process of making breakfast discovered that during the previous night’s kitchen cleanup, I’d neglected a single item: the lid to the steamer. It was face down, one edge on the stove top and the other on the counter, thus giving it a slight tilt. When I picked it up, I noticed a lovely patten of water droplets on the inside of the lid.
Some days I spent a lot of time doing associative reading, where one text leads me to hop laterally to another text, and so on. I find this pleasurable, but often, after a few hours, have little sense of what I have learned.
Today I am going to try to track, at least partially, the path of my attention.
I did not begin here, but a good starting point is Taleb.
Bright and early, well, somewhat early, we visited the Minneapolis Institute of Art to see Botticelli and Renaissance Florence: Masterworks from the Uffizi. I was struck by three things.
I observed a curious phenomenon on my run today. I have been unable to find an authoritative account or name for it, so I will call them snow crenellations.
One thing I enjoy doing is photographing natural patterns. Something about the patterned chaos of nature is very attractive to me. Here are four images from our most recent trip to the north shore of Lake Superior, taken in May 2022.
Here are two images of foam in a backwater on the shore. I like how the precussion of the waves has built up ridges upon ridges of foam – in the first picture it looks almost woven. I like, too, that the threads of foam are in turn inflected by the flow of the backwash as it interacts with shore and rocks.
Here is another image from the same trip. It is a pattern of lichen on a rock. I presume, but do not know, that there are different colonies of lichen contending for the same patch of rock/sun, and that they have arrayed defenses against encroaching colonies creating a bordered patchwork, like a small continent of countries :
From October 2019, brought to mind by the lichen, are some images of a fungus on Maple leaves in Yosemite Valley. I’m intrigued by the speckled brown centers, which I imagine contain sporangia, surrounded by the halos of green (chlorophyll?). These different fungal colonies seem less hostile to one another than in the case of the lichen, since they appear to sometimes merge.
Two weeks and change have passed, and here I am again.
The notable events for the last couple of weeks include ‘graduating’ from physical therapy, a trip to the north shore, and… well, I think not much else.
I sporadically read a weekly newsletter called Reasons to be Cheerful. RtbC was founded by, and still features writing by, David Byrne, singer, songwriter, etc. As its title suggests, it is a purveyor of hopeful news, something that I’ve welcomed over the last few years.
This week there was a link to a story on another blog that really stuck a chord. It is about the work of a street artist who ‘repairs’ pavement by embedding mosaics in damaged areas. (The full article can be found here: https://www.thisiscolossal.com/2022/02/ememem-pavement-mosaics/)
