Fact: I fucking love talking about my chosen field ofs tudy. Additional fact: learning to interpret science to a more-or-less lay audience is a fucking important skill. Problem: I haven't the faintest idea where to start, most times. Solution: ask me shit!
help I am suddenly a 5 year old who needs to know: if it's solid then why is it lava all liquid-y when it comes out of the volcanoes?
Pressure! Here's a nice stereotyped generic phase diagram - I would have pulled out an actual geological phase diagram, but those are a mess and a half. So you're starting at high temperature and high pressure in the mantle and are very definitely solid, so put your "start point" a little bit to the left of letter D up there, all the way in the solid field. From that start point, there are two ways to get to the liquid field. You can increase temperature (difficult), or you can decrease pressure (easy, just go shallower). The pressure at the surface is a hell of a lot less, so something that's hot at the surface will be liquid, while the same thing at the same temperature (or higher!) would be solid down in the crushing pressures of the mantle. Also, liquids are less dense than solids (dihydrogen monoxide georg is an outlier adn should not have been counted) so any liquids you do have are gonna float up to the surface. Now, where you get those liquids in the first place is a bit of a different question, which I can also go into if people are interested.
ARE THERE DRAGONS UNDER THE EARTH. So... why does flint happen in some areas with sedimentary rocks, but not others? This may be a silly question.
Probably not, but there's some running around on the surface. As to flint (or chert, which may or may not be a synonym to flint, a hypernym of flint, or a separate but related thing, depending on who you ask) it's a microcrystalline variety of quartz - which logically enough means that it's made of lots and lots of interlocking microscopic crystals, rather than the bigger crystals you are probably thinking of when I say "quartz." (sometimes the individual crystals are too small to even see with an optical microscope, in which case it gets called cryptocrystalline). I believe our current best model for the formation of flint and chert is that they crystallize from dissolved silica (not something one sees every day), so the places you can find them would be controlled by the places you could expect to get that. The best source is going to be biological - things like sponge spicules, diatom frustules and radiolarian tests which are a) made of more amorphous opaline silica which is marginally less non-reactive than crystalline quartz (and thus more willing to dissolve) b) already microscopic and c) will occur in huge masses all in one place from things like algal blooms and sponge reefs. I believe there are non-biological sources as well, especially silica-rich volcanic ash and clay-sized grains of quartz that have been broken down small enough to overcome quartz's famous resistance to chemical weathering or dissolution. Then either you get an accumulation of these tiny silica grains and enough dissolved silica to precipitate quartz cement between them (cf. radiolarian chert beds), or you get dissolved silica concentrated in one point and precipitating those stereotypical flint nodules, or you get dissolved silica rich water flowing through pore spaces of preexisting rock and replacing what was there before with silica (doesn't usually get called flint or chert in that case, ime). This last process is one of the ways that you get fossilized bone or wood or things that don't generally stick around, and will also replace shells and whatnot that would have stuck around anyways, making them much harder and more chemically stable at the cost of erasing some detail. So in summary: if you want flint or chert, you want the area to have been underwater at some point during or after the creation of the sedimentary beds you're looking at, you want it to be relatively deep marine or alternately near a volcano that was spewing a lot of silica, and you want the fluid chemistry and flow to be right to dissolve some silica, transport it, and crystallize it where you want it. Don't got that, don't get flint.
ROCKS. Also wixwixia. An author I'm very fond of wrote a cosmic horror story that utilizes geology. Written by a geologist too! Called Threshold: A Novel about Deep Time by Caitlin R. Kiernan if you're curious.
Oh my fucking god I just realized your signature is a pun. Why are things like quartz so widely varied in color? Also what is up with crystal caves and how dare they look like shit out of a video game while apparently being dangerously warm.
is everything made of quartz? because i am like pretty sure everything is quartz. -points at a rock- is that a quartz
Oh dude, I've got a little bit on the Mars question! Planets only have geological activity if they have enough heat, and for a variety of reasons, Mars lost its heat much faster than Earth. If I remember correctly it's partly because of Mars' lack of atmosphere, it being so much smaller than Earth, and so much farther from the sun. Possibly something to do with its magnetic field? I think magnetic fields have something to do with the molten core circulating inside the planet but don't quote me on that. So Mars no longer has a molten core! Without that heat, the mantle doesn't have the convection currents of rising and lowering heated and cooled rock, so the tectonic plates don't move. Mars used to have plate tectonics! But everything cooled off and it doesn't anymore.
ehehehehe gotcha Color in minerals is a property of which wavelengths of light are not absorbed (and are instead transmitted through the mineral or reflected back from it). There's a couple different things that can cause certain wavelengths of light to be absorbed or not, but the most relevant for our purposes here are things called chromophore ions. These are ions, usually of various transition metals in the periodic table, that strongly absorb certain wavelengths of light, thus pigmenting everything around them the color of white-light-minus-those-wavelengths (pull out red, get cyan, &c). The exact color is determined by a thing called crystal field theory, which sounds like the hippiest woo bullshit ever, but is actually a bunch of unutterably technical chemistry and physics that I don't really feel qualified to try and explain. Suffice to say that it depends on the element in question (Cu vs. Fe), the charge of the ion (Fe2+ vs. Fe3+) and on the surroundings of the ion in the crystal structure (messy). So you've got some minerals, like malachite, that have one of those kinds of ion in their chemical formula ( Cu2CO3(OH)2 ). Cu2+ generally makes things blue or green and so malachite is always green. (the occasional blue you see there is actually azurite, a different mineral made out of the same stuff as malachite but in a different ratio and organization. They often occur together and one can turn into the other under the right conditions, which is why you sometimes see medieval paintings with green skies - the azurite paint has altered to malachite) The technical term for this is "idiochromatic" and it's the only time when color is actually helpful in identifying a mineral. And then you've got minerals like quartz (SiO2) which... don't. But quartzes are clearly not colorless! What's happening there is that since perfect, pure quartz is colorless (no chromophores) the actual color of any sample is pretty much anyone's game. Trace impurities of chromophore ions? Bam, color. Structural defects where an oxygen is missing from the crystal structure and there's just some free electrons hanging out where it should be to keep the charges balanced? Bang, different color. Here's a pretty good website that goes into more detail on the optics of the different mechanims of coloring. You can also get variation in color in a situation like olivine where the chemical formula ( (Mg,Fe)2SiO4) contains chromophore ions, but there's variation in the exact composition (you need two ions of either Mg2+ or Fe2+ but whatever ratio you have, it's olivine) so you get a variation in color between Spoiler: Fayalite (iron-rich olivine) vs. Spoiler: Forsterite (magnesium-rich olivine) With a whole range of intermediate compositions and colors. (plus potential effects on color by impurities and whatnot)
Important geology question: What would be your gemsona? More seriously, why do shimmery stones like opals and labradorite do the thing? (As for chatoyancy, asterism, and aventurescence, they're all caused by shiny inclusions, I think?)
What is up with platinum-fused quartzes, why do they do the weird oily-rainbow-iridescence thing? (Unrelated to thread: do you know where the main rocks thread went? I can't seem to find it in general chatter D:)
*kicks thread to get it working again* Clinohumite or possibly diopside. This is getting into optics stuff that I'm not really the best person to ask, but I believe it's diffraction bullshit from layers of amorphous silica globs (in opal) and apparently weird exsolution bullshit in labradorite? I can get into "what the fuck is an exsolution" if you want. Fig 1. globs of amorphous silica, in layers, doing diffraction bullshit to look pretty Also worth noting that the iridescent fire of opals is a different thing than opalescence, which is where your transmitted and scattered light are different colors (orange and blue, respectively, usually) so your potch opal looks blue in bulk, but casts orange light on it's shadow, and has orange reflecting off the back of the rock back through it towards you. This is apparently related to why the sky looks blue during the day but red at sunset, but again. Optics. Not my field. Fig 2. Like so Fig 3. If your amorphous silica globs aren't stacked up all nice, you get opalescence but no fire Fig 4. Bonus round: calcium carbonate plates in mother of pearl doing the same "stacked up all nice to diffract and look pretty"
