Rocks & Minerals B/C

[sofossils]

Does anyone know how to tell apart Malachite, Olivine, and Epidote when in massive and unpolished form?

[paleonaps]

Hi! Remember me?
I was just looking through the wiki and I saw that it has Opal and Quartz as Oxides. However, the Simon and Schuster guide, the Internet (i.e. Wikipedia), and my memory say that they are actually Silicates. I changed it on the wiki, but I figured I'd ask if it was a mistake or if they were reclassified or something. I just want to make sure that it's accurate.

[aim4me26]

Hi! Remember me?
I was just looking through the wiki and I saw that it has Opal and Quartz as Oxides. However, the Simon and Schuster guide, the Internet (i.e. Wikipedia), and my memory say that they are actually Silicates. I changed it on the wiki, but I figured I'd ask if it was a mistake or if they were reclassified or something. I just want to make sure that it's accurate.

Lol, hi Naps. And yeah, I think you're right.

[allisonc524]

So, I've got state tomorrow, and was just told today that I'm on rocks and minerals. What can I study in that short amount of time? No one expects me to do well, but I'm hoping I might surprise my team...

[Skink]

Maybe either...

1. Try to learn to identify by sight a few obscure minerals your partner may not know e.g. kaolinite, sphalerite...

2. Try to make sense of Bowen's reaction series and Moh's hardness scale. These are effectively reading charts, so you could try to quickly get really familiar with these and ignore sample ID, which your partner should be well prepared for at this point. You could throw in crystal systems if you wanted to, but that's less important in a time crunch.

Hi! Remember me?
I was just looking through the wiki and I saw that it has Opal and Quartz as Oxides. However, the Simon and Schuster guide, the Internet (i.e. Wikipedia), and my memory say that they are actually Silicates. I changed it on the wiki, but I figured I'd ask if it was a mistake or if they were reclassified or something. I just want to make sure that it's accurate.

Look at the chemical formulas. Quartz is easy, SiO2, and, looking up opal, it's derived from that. The silicate Wiki page says silicates are SiO4 tetrahedra and that, for that reason, SiO2 is sometimes classified as a silicate. Calling it an oxide will never completely be wrong because it IS an oxide. Whether grouping it as 'silicate' is more correct or not, well, the jury's still out, it seems.

[kalithepianist]

can somebody explain Bowen's Reaction Series? i can't really find a simple explanation for it and i'm not really seeing how it's helpful for this event .___.

[tuftedtitmouse12]

Hi! Remember me?
I was just looking through the wiki and I saw that it has Opal and Quartz as Oxides. However, the Simon and Schuster guide, the Internet (i.e. Wikipedia), and my memory say that they are actually Silicates. I changed it on the wiki, but I figured I'd ask if it was a mistake or if they were reclassified or something. I just want to make sure that it's accurate.

Lol, hi Naps. And yeah, I think you're right.

Will second it...too lazy to hunt down my rocks field guide floating around somewhere.

[quizbowl]

can somebody explain Bowen's Reaction Series? i can't really find a simple explanation for it and i'm not really seeing how it's helpful for this event .___.

So imagine I'm a big ol' volcano. RAWR I GOTS MAGMA.
Discontinuous: When magma cools, the minerals that form will form in a very specific way. First olivine forms at the hottest temperature, and as the temperature goes lower, new minerals start to form (pyroxene-> amphibole -> biotite). Eventually, at a very cool ~850C, it forms orthoclase, muscovite and quartz. It's pretty helpful - you can tell that rocks that are mafic tend to form at hotter temperatures than felsic rocks, and the respective minerals in each correspond to their position on the reaction series. By the logic, you'll never find a typical igneous rock containing both olivine and quartz crystals (unless something funky is going on).

Continuous:: Along similar lines, but we're looking at the Ca/Na ratio of the magma (mafic contains lots of calcium, intermediate contains lots of sodium). Essentially, at the highest temperatures it'll be rich in Ca-feldspar, and as you cool, you'll have more Na-feldspar. It also converges to the orthoclase-muscovite-quartz point.

If you understand how the Bowen's Reaction Series works, you can figure out why there is differentiation among igneous rocks.

[zimmy1235]

I'm looking at chert and chalcedony, and was wondering if someone could explain the terms microfibrous and microcrystalline, and possibly cryptocrystalline as I don't totally get their difference and how they apply to each of the previous specimens.

[Shad160]

I'm looking at chert and chalcedony, and was wondering if someone could explain the terms microfibrous and microcrystalline, and possibly cryptocrystalline as I don't totally get their difference and how they apply to each of the previous specimens.

From my understanding, microcrystalline describes a crystal habit that is minuscule and only visible through a microscope, microfibrous is a fibrous crystal habit that can only be viewed under a microscope, and cryptocrystalline has a crystal habit that can only be viewed through polarized light (and a microscope, at that). They're all relatively minute differences, term-wise.

For their role in Chert and Chalcedony, the terms are just used to describe the different varieties that are possible for the crystals

(I've also only been on this event for <1 month, so if someone has a better understanding please feel free to chime in)