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This circuit diagram has a symbol I've been unable to identify, which I've indicated with a stylish green arrow. I'm guessing some sort of capacitor based on the uF measurement, but I haven't been able to confirm that in my search through general circuit symbol lists or for capacitor symbols. Can someone clue me in?

circuit diagram with unknown symbol

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It's an electrolytic capacitor. These are polarized, as the + sign also indicates. This is a less common symbol. Below are the more common ones, European on the left, American on the right.

enter image description here

Compare to the symbol for a non-polarized capacitor:

enter image description here

Note: I think the American symbol for a non-polarized cap is a bad one; it suggests that there is some kind of asymmetry where in reality there isn't one.

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From the comments it appears that the supposedly American non-polarized symbol is less common than I thought. I can only speak from my experience, and like I also said in comment, it could be that I've been looking mostly at older schematics (not the tubes, I'm not that old).
I found this schematic within a minute:

enter image description here

C2 might be an electrolytic (it won't be, will have a too low capacitance), but look at variable capacitor C1.
Also this page.

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Browsing through more symbols encountered also this weirdo (the one on the right):
enter image description here

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    \$\begingroup\$ I have to admit, I have seen about 30 symbols for drawing capacitors. I am actually used to just drawing two straight lines. I only draw a curved line if it is polarized, I always thought of the curved mark as a sign for polarity. I probably never follow standard though. \$\endgroup\$ – Kortuk Jul 17 '11 at 5:30
  • \$\begingroup\$ I don't think one is better than the other. I typically use the European version for non-polarized and the American version for polarized. That way I never have to use +. Although sometimes I write the + for good measure.... \$\endgroup\$ – Origami Robot Jul 17 '11 at 5:33
  • \$\begingroup\$ @OrigamiRobot - that would be a problem for me. I live in Europe and use the European symbols. I wouldn't know which side was the + on the American symbol unless I looked it up. \$\endgroup\$ – stevenvh Jul 17 '11 at 5:40
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    \$\begingroup\$ I'm American, and haven't ever seen the Straight/Curved line cap symbol for a non-polarized cap anywhere I have worked. I don't know why you think it's an American thing. Frankly, it's a terrible way to do the schematics. \$\endgroup\$ – Connor Wolf Jul 17 '11 at 6:56
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    \$\begingroup\$ The straight/curved cap symbol, without polarization, was common on Radio Shack schematics I saw in the 70's and 80's. Nowadays, we mostly use the two-parallel-lines symbol, not the two-filled-rectangles symbol that Europeans use. At work, we require polarity markings ('+' in the case of capacitors) on schematics. Curved/straight lines don't count since a lot of the people who read the things don't remember which is positive. \$\endgroup\$ – Mike DeSimone Jul 17 '11 at 13:34
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Regarding the non-polarized symbol with one curved side, the curved side represents the OUTER foil in a rolled foil capacitor. In a grounded capacitor, one would want the outer foil grounded.

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