Preliminary Notes On The Geology Of Opal Formation

the birth of opals: not too deep in the bedrock that makes the Earth there are all sorts of cracks.  the Earth is always heaving and sighing and cracks form.

there is water also either soaking down from above or welling up from below.  patchy heat sources can also send water seeping in from above back up.

these waters will then dissolve the minerals in the rocks.  the most common minerals in rocks are silicates: quartz, feldspars, mica, clay...

so these waters become enriched in dissolved silica.  silica is interesting stuff.  silicon dioxide can arrange itself into all kinds of interesting structures: strands, rings, flat hexagonal networks...  these molecules come with positively charged and negatively charged ends, that make them stick together tentatively like magnets into even more structures.

the way the silica structures attach to each other is modulated by the pH of the waters.

i don't really understand this... i must review my book:
"Silica and Me", by Guy Alexander.  an excellent first person account of the adventures of a rookie research chemist in industry as he begins to solve some problems in silica chemistry.  along the way he explains in a clear fashion a lot of interesting chemistry

(it appears to be out of print but a few copies appear to be available from amazon at the moment)



under certain conditions of temperature, pH and other dissolved ions like carbonates and sodium etc... the silica will precipitate out as crystals or spheres i don't know what selects for either...  perhaps crystals precipitate out only in purer silicon dioxide, while being mixed with water produces a kind of silica tetrahedron strand - water chaos...

now the microspheres 150nm to 1000nm wide will be in suspension and will be negatively charged and will repel each other.  by modulating the ph and ion content and concentration of the spheres some more the degree to which the spheres can contact can be modulated.  under some conditions they will want to contact the least and will thus form long linear strands.  at point of contact though, chemical bonding can occur.  as concentration goes up these strands can precipitate and line up, again contacting the least amount to make perfect cubic packing of the spheres

if  there are spheres of different sizes... they will tend to come into closer contact with each other... (draw a picture) (actually, if there are small spheres that can fit between the spaces in the larger sphere packing that would be the least favorable situation, but a bunch of spheres of SLIGHTLY different size would produce less perfect packing and so less contact? hmm this is puzzling, requires more thought) so perhaps electrostatic repulsion alone can cause spheres of uniform size to precipitate together...

so you can have a multistrand strands of uniform sized spheres of one size next to another multistrand strand of uniform spheres of another size...

it is the regular arrangement of the these uniform spheres that forms a diffraction grating that causes the color play in the opals.  so you can have streaks of different color/opalescence this way

other processes that can effect opal formation are other trace minerals to form nuclei around which the microspheres first precipitate out.

another process is sorting of sphere sizes by filtration through clays by pressurized silica solutions.  the pressurization could come from volcanic heat or from other clays.  some clays will absorb water and this causes them to swell, so they will exert pressure on adjacent layers of silica solutions...

another factor that can effect the precipitation of microspheres is if cooler waters or waters of different pH seep down and contact the warm waters rich in dissolved silica.

another factor may be bacteria living in the water filled cracks.  they may also be able to modulate chemical conditions around themselves to effect the formation of these microspheres.



some references:

general
opal wiki


where i got some details from:
THE ORIGIN OF PRECIOUS OPAL: A new model
Byron Deveson

Ramblings On Vertebrate Mating Dances and Rhythm

a few weeks ago i was watching israeli folk dancing, and wondering about cichlid fish, and birds.

prospective mates sizing each other up for skill, genetic health and compatibility. the fact that someone could have memorized dozens, HUNDREDS of complex synchronized dance movements. like the brown thrasher and his 2000 songs. the fact that you can synchronize with another person to that level of accuracy.

the cichlids that have to spend many weeks together at the risky consuming task of raising kids in a three dimensional risky environment. the females probably got a whole season invested in this, so it's got to be done RIGHT! so they gotta be sure they are compatible physically. they go through elaborate sizing each other up dances:

http://ib.berkeley.edu/labs/barlow/book.html

over 1000 different kinds... these guys lay eggs and then care for them, then care for their young. some build nests for the kids, some keep the eggs in their mouths, some excrete a kind of 'milk' on their skins that the babies feed off of. variations of males, females caring for the kids.

it's alot of work and so the males and females have a complex time sizing each other up during courtship to decide wether they will work well together for the coming weeks/months of raising kids. big investment in time and energy.

fascinating book. fascinating fish.

but all the vertebrates going through these elaborate mating routines. do they really make important choices? how important are the choices? how MUCH difference do they make? enough to warrant the elaborate games?  wonder how you test it.


* * *
how do the ones that mate for more than one season compare? do song birds mate for more than one season? scrub jays? thier male kids help 'em raise up another batch, so... like wolves. not elephants. not chimps. not dolphins?

and humans wouldn't if it weren't for the fact that the guys stay on to help raise up a kid that takes years... so he ends up having more? but chimp kids take years... the sisters help.

hypothesis on why male mates stick around for childraising in Humans: unlike in chimps the older sisters aint mature enough to help out by the time the next kid comes along!


 * * *
so write about rhythmic mammals.  what's it mean:?  social function, even the women?  interesting.  one doesn't usuually think of it.  yet many mammal societies are women elephants and dolphins and chimps  three different groups.  not wolves.  not carnivores, curious!  woops dolphins are carnivores.  hunters?  or grazers?

so whence the rhythm?  what other mammals?  birds don't do it!  one thinks of animals doing something rhythmic as pathological!  really?  the polar bear going rouund and round his tank.  a sick fish shimmying..



 * * *
hmmm the place of human music in human evolution...

one thing i would note, is that while bird "song" is very complex (see my posts about Kroodsma's book) it is VERY different than our long winding narrative songmaking.

lots of aspects to our music. the songs, the songtructures, the long narratives, the harmonic structures, and the rhythm

our music and our language facilities seem to be related..

do octopi do anything like music?

music is hierarchical, so is language, do narratives tend to have nested heirarchies, or are they "and then this happened and then that happened" or are they more tangled...


20JUN2008
i can think of some specifics: narratives long winding narratives. so far we know no animal that can weave long stories stanza after stanza with subtle variations, like shakespeare or charlie parker.

mockingbirds? subtle variations, but i don't know if they are telling a narrative.

whales? i don't know what they are doing.

honeybees? (search forum) their narratives are very short and finite.



communal bonding:

i know of no other species that gets together in communities as populous as ours. HUNDREDS of millions? in nations? in relgions in isms, in brand loyalty...

no ant community goes to 100 million

exacerbating this is our propensity to communal ecstatic states. we whip each other into frenzied mobs that can build empires or storm empires.

has something to do with rhythm



rythm?

usually in other animals, behaving in a mechanically rhytmic state is a sign of sickness?

i know of no other animal that keeps rhythm like we do, creatively, subtly but STEADILY, no birds sing in the rhythm that human musicians and ecstatic dancers do...

this relates to the fact that we use steady rythm and rythmic breathing to reach ecstatic states.

when we reach these rythmic ecstatic states in mobs we march across the planet and take over...

...
not extended period, that i think is the key point! humans will do rhythm for HOURS, KEEPING rhythm, but CREATIVELY. god, i miss the pots and pans man down in the subway at times square! and to the point of reacing ecstatic states.

do any animals do THAT?

head bobbing of iquanas, is that really in good rhythm?

i'm talking:

tony williams playin' live at the plugged nickle with miles davis:

http://www.youtube.com/watch?v=dYSaX-za64E

it's rhythmic it's precise but fluid, he's thinking INSIDE the rhythm, (totally unlike those frogs you heard, unless i'm mistaken) check out:

http://www.amazon.com/gp/product/B00138F8RS/ref=dm_sp_alb

amazing shit.