Rocks & Minerals B/C

[inluvwyth_WANTED]

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.

since you are the division C Rocks event supervisor,do you know who is running division B?

[kalithepianist]

Can somebody explain the difference between hematite and magnetite, except for the fact that magnetite is - obviously - magnetic?

[Shad160]

Can somebody explain the difference between hematite and magnetite, except for the fact that magnetite is - obviously - magnetic?

I'd immediately try and look at streak, as hematite's is a distinct red and magnetite's is blacker. If streak plates aren't available, then there are a few other options- Hematite is a tad more dense, harder, and will generally appear redder than magnetite. If you google image the specimens in different tabs, you can see the different crystal habits that one has over the other, such as Magnetite's Octahedral habit and the globules that Hematite can form. Other than that, I guess it would become a matter of staring at enough examples of either specimen to just be able to innately tell the difference.

[quizbowl]

since you are the division C Rocks event supervisor,do you know who is running division B?

If I did, would it matter?

[inluvwyth_WANTED]

No...just wondering...

[tuftedtitmouse12]

Can somebody explain the difference between hematite and magnetite, except for the fact that magnetite is - obviously - magnetic?

I would also say that magnetite is fairly heavy. Of course, this only works if you have specimens available.

[gneissisnice]

Can somebody explain the difference between hematite and magnetite, except for the fact that magnetite is - obviously - magnetic?

Streak is by far the most useful property for identifying hematite. It's the only mineral with a reddish-brown streak. If you don't get a streak plate provided (which would mean a terribly written event), magnetite is always black, but hematite tends to show some reddish colors, and its specular form looks totally different; it has a metallic luster.

Also, specular hematite can be magnetic, so don't be fooled into thinking that it must be magnetite if it's magnetic. As far as I know, only specular hematite is magnetic, and you won't ever confuse the specular form with magnetite.

[piimasta314]

Hi,
I'm fairly new to this event. Do you know if they usually use real samples?
I went over a lot of the marathon questions and I had a really hard time with the pictures; the angles and lighting kind of threw me off on some really easy ones.
Also, this is the first time I've been state. How are the state tests for CA? Do the stations go really fast? (Regionals gave us about 1:30 per question.) And is it mostly identification or mostly theory?

[darkdeserthighway]

They usually use real samples.

[vulcanologist1234]

It is mostly a reasonable time over 2 minutes