Symbol: Center of Mass (dowelpin)

Does anyone know of the symbol used for the center of mass in physics? Typically it is a circle with two quadrants shaded in. Unfortunately I can't find this in the standard LaTeX symbols PDF or on Detexify.

Is there a predefined command for this symbol or some other way I could get it?

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In general, Scott Pakin's LaTeX comprehensive symbol list has a vast amount of symbols supported using various packages in LaTeX. See the documentation for more information. –  Werner Jul 19 '11 at 3:00
...sadly it's not in there... :( (yet?) –  Werner Jul 19 '11 at 3:12

I don't think it's available as a proper symbol, but you could use TikZ to draw it. By using the units em or ex, the symbol will scale corresponding to the surrounding text.

\documentclass{article}

\usepackage{tikz}

\newcommand\centerofmass{%
\fill (0,0) -- ++(0.4em,0) arc [start angle=0,end angle=90] -- ++(0,-0.8em) arc [start angle=270, end angle=180];%
\draw (0,0) circle;%
}%
}

\begin{document}

Center of Mass: \centerofmass

\Huge It scales! \centerofmass

\end{document}

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